What qwen3.8-27b did

Let me plan this out. I need to build a one-page marketing site for "Nimbus Notes" — a note-taking app that syncs across phone, laptop, and web.

Structure:
1. Top bar — product name + 3 links (Features, Pricing, and... wait, "links to the three sections below" — the sections below are Hero, Features, Pricing. But the top bar is above the Hero. So "the three sections below" probably refers to Features, Pricing, and... hmm. The page order is: top bar, hero, features, pricing, footer. "Links to the three sections below" — the sections below the top bar are hero, features, pricing. But linking to the hero is a bit weird. Actually, the three main sections are Features, Pricing, and... Footer? The footer isn't a section. Let me think: the sections are probably Features, Pricing, and Hero. Or maybe I should treat "sections" as Features, Pricing, and... hmm.

Actually, re-reading: "Top bar — product name and links to the three sections below." The sections below the top bar: hero, features, pricing. That's three. But linking to the hero is odd. Alternatively, I could add an "About" or keep it simple: Features, Pricing, and Contact (footer). Hmm.

The safest thing is: nav links to Features, Pricing, and... the hero is a section too. But a "Home" link pointing to the hero is common. Let me do: "Features", "Pricing", and "Home" (pointing to the hero/top). Hmm, but "links to the three sections below" — home/top is a section (hero). Let me label them: Features, Pricing, Home? That ordering is weird.

Alternative: make the hero a section with id="top" or id="home". Nav: Home, Features, Pricing. That's three links to three sections below the top bar. That works and makes sense.

Actually wait — the footer has three links. The top bar links to the three sections below: hero (Home), Features, Pricing. Let me go with that.

2. Hero — heading, one-sentence subhead, primary CTA button, secondary text link. Visual: I'll make an SVG mock of the app's interface — a note card with a sync icon showing three devices (phone, laptop, web). That would be a nice touch: an SVG illustration showing a note syncing across three devices. Let me draw a clean SVG: a laptop in the center, a phone on the left, a browser window on the right, with a cloud above and sync arrows/dots connecting them. Or a single "app window" mock with a sidebar and note content, plus a small floating phone. Keep it tasteful.

3. Features — exactly three, each with an SVG icon, a short title, and two sentences of copy.

Feature ideas:
- "Sync that just happens" — real-time sync across phone, laptop, web.
- "Fast to open, fast to write" — performance.
- "Yours, encrypted" — privacy/encryption.

4. Pricing — Free, Pro $8/month (recommended, visually marked), Team $20/month. Each tier has 4 bullet points and its own button.

5. Footer — copyright line + 3 links.

Requirements:
- Deliberate design: one type scale, one spacing scale, small consistent palette.
- Responsive at 1280 and 375. Top bar collapses sensibly at narrow widths — no horizontal scroll.
- Interactive: smooth scroll, hover + focus states.
- Accessible: landmarks, one h1, heading order, AA contrast.

Let me pick a palette. "Nimbus" evokes clouds/sky. Palette:
- Ink (text): deep navy #16233B or #1B2A4A
- Primary: vivid blue/indigo, e.g. #3E63DD or #2F5FE0. Let me go with a cloud-blue theme:
  - Background: #F7F9FC (very pale blue-gray)
  - Surface: #FFFFFF
  - Ink: #17233A (dark navy) — AA on white: contrast of #17233A vs white is very high, fine.
  - Muted text: #4A5A75 — check contrast on white: #4A5A75 vs #FFFFFF... let me estimate. Luminance of #4A5A75: r=74, g=90, b=117. Relative luminance ≈ 0.2126*lin(74/255) + 0.7152*lin(90/255) + 0.0722*lin(117/255). lin(0.290)= (0.290+0.055/1.055... formula: if c<=0.03928 then c/12.92 else ((c+0.055)/1.055)^2.4. 74/255=0.2902 → ((0.3452)/1.055... wait (0.2902+0.055)/1.055 = 0.3272^2.4. ln(0.3272)≈-1.117, *2.4=-2.681, e^-2.681≈0.0685. g: 90/255=0.3529 → (0.4079/1.055)=0.3867^2.4: ln≈-0.950, *2.4=-2.280, e≈0.1023. b: 117/255=0.4588 → (0.5138/1.055)=0.4870^2.4: ln≈-0.7195, *2.4=-1.727, e≈0.1777. L = 0.2126*0.0685 + 0.7152*0.1023 + 0.0722*0.1777 = 0.01456 + 0.07317 + 0.01283 = 0.10056. Contrast with white: (1.0+0.05)/(0.10056+0.05) = 1.05/0.15056 ≈ 6.97. Passes AA (4.5) for normal text.

  - Primary: #2F5FE0? Let me check white text on it: luminance of #2F5FE0: r=47/255=0.1843 → (0.2393/1.055)=0.2268^2.4: ln≈-1.484, *2.4=-3.561, e≈0.0284. g=95/255=0.3725 → (0.4275/1.055)=0.4052^2.4: ln≈-0.9034, *2.4=-2.168, e≈0.1144. b=224/255=0.8784 → (0.9334/1.055)=0.8848^2.4: ln≈-0.1225, *2.4=-0.294, e≈0.7453. L=0.2126*0.0284+0.7152*0.1144+0.0722*0.7453=0.00604+0.08182+0.05381=0.1417. Contrast with white: 1.05/0.1917≈5.48. Passes AA. Good.

  - Accent (soft): #DCE7FB or #E3EDFF for tints.
  - Maybe a secondary accent for the "recommended" badge: a warm color? Or keep it monochromatic blue + one warm accent like amber #F5A524? A small palette: ink navy, primary blue, pale blue tint, white, and maybe a soft sky #7FA6F5 for illustration. Let me keep it:
    - --ink: #182642
    - --ink-soft: #45536E (check contrast: r=69, g=83, b=110. Similar to above, ~6.5:1, fine)
    - --blue: #2E5BE6 (close to the #2F5FE0 I checked, fine)
    - --blue-deep: #1E3FAE (for hover)
    - --sky: #E8F0FE (tint background)
    - --paper: #FFFFFF
    - --mist: #F5F8FD (page background)
    - --line: #D8E1F0 (borders)

Type scale: use a modular scale. Base 16px. Scale ratio ~1.25 (major third): 16, 20, 25, 31.25, 39, 48.75... or simpler: define sizes:
- --text-xs: 0.8125rem (13px)
- --text-sm: 0.9375rem (15px)
- --text-md: 1rem (16px)
- --text-lg: 1.25rem (20px)
- --text-xl: 1.5625rem (25px)
- --text-2xl: 1.953rem (~31px)
- --text-3xl: 2.441rem (~39px)
- --text-4xl: 3.052rem (~49px)

That's a 1.25 scale. Good — "one type scale."

Spacing scale: 4px base: 4, 8, 12, 16, 24, 32, 48, 64, 96. Use CSS variables --s1..--s7 or named: --space-1: 4px ... Use rem: 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, 6.

Font: system stack (offline, no external fonts): -apple-system, "Segoe UI", Roboto, Helvetica, Arial, sans-serif. For display, I could use the same stack with heavier weight and tighter letter-spacing. Keep it one family for consistency.

Layout:
- Top bar: sticky, white background with a subtle border/shadow on scroll (JS adds a class). Contents: logo (SVG cloud + wordmark), nav links (Home, Features, Pricing), and maybe a small "Get Nimbus" button on the right? Spec says product name and links to three sections. A CTA in the top bar is extra but common. To be safe and clean, I'll include a compact "Get the app" button in the top bar on wide screens, hidden on narrow... actually, the spec is precise: "product name and links to the three sections below." Adding a CTA button is a design choice and fine, but let me keep the top bar minimal: logo + 3 links. On narrow screens, collapse the nav into a details/menu button? "The top bar must reflow or collapse sensibly at narrow widths." At 375px, logo + 3 short links (Home, Features, Pricing) might fit: "Nimbus Notes" logo ~130px + 3 links ~90px each = too tight. Options: hide the wordmark text and show just the cloud icon at narrow widths, letting the links fit. That's a sensible collapse. Or a hamburger menu. Hamburger with JS toggle is more "interactive" and shows craft. But it adds complexity; still fine. Hmm — a hamburger adds an accessibility burden (aria-expanded, etc.) but I can do it properly.

Let me do this: at ≤640px, show a menu button (hamburger) that toggles a dropdown panel with the 3 links. Use aria-expanded, close on link click, close on Escape. That's a sensible collapse. Also, keep the wordmark visible.

Actually, a simpler alternative that avoids JS menu bugs: at narrow widths, shrink the logo to icon-only and keep the links visible (Home · Features · Pricing are short). At 375px: icon 28px + gap + 3 links. "Features" at 15px is ~62px, "Pricing" ~52px, "Home" ~44px, gaps 16*2... total ≈ 28+16+44+16+62+16+52 = 234px + padding 32 = 266px. Fits comfortably in 375. Hmm, that's actually quite comfortable. But is that "sensible reflow"? Yes — reflowing to icon-only logo is sensible. But a hamburger is more standard. The requirement says "reflow or collapse sensibly" — either works. Let me go with the hamburger for craft points and to demonstrate interactivity; I'll implement it carefully with proper ARIA.

Hmm, let me weigh it: the hamburger menu requires JS state management, focus handling, Escape handling. It's a well-trodden path; I can do it. Let me do it: a button with aria-controls, aria-expanded, a nav panel that slides down under the top bar. Close on link click, close on Escape, close on resize to desktop.

Smooth scroll: CSS `scroll-behavior: smooth` on html + `scroll-padding-top` for the sticky top bar offset. Also respect `prefers-reduced-motion` (disable smooth scroll and animations). JS is optional; CSS smooth scroll is simplest and most robust. I'll also add JS to close the mobile menu on click.

Hero visual: SVG mock. Let me design a nice illustration: a cloud with three device screens (phone, laptop, browser) and sync pulses. Or an app window mock: a rounded rectangle window with a title bar (three dots), a sidebar with note list items, and a note area with text lines and a "Synced" chip. Plus a small phone overlapping in the bottom-right showing the same note — conveying sync. That would be a strong, concrete visual: "the same note on two screens."

Let me sketch the SVG (viewBox 0 0 560 440 or so):
- Background: a soft blob/cloud shape behind (very pale blue).
- Laptop: rounded rectangle body with a screen; screen shows a note app: top bar with dots, sidebar column with 3-4 note rows, main area with a title line and text lines.
- Phone: rounded rectangle with a notch, showing the same note (title line + text lines), a "Synced" pill with a check.
- Cloud above with a small sync arrow (circular arrows) between devices.
- Dashed arcs connecting the devices to the cloud.

Colors: white surfaces, #D8E1F0 lines, blue accent #2E5BE6, sky tint #E8F0FE, ink lines #182642. Add subtle shadows with an SVG filter, or just a darker offset shape (simpler: use feDropShadow filter — fine in modern browsers).

I'll build the SVG carefully with groups and comments. Keep it clean and geometric.

Feature icons (SVG, 24-32px stroke style, consistent stroke width 2, rounded caps):
1. Sync icon: two curved arrows forming a circle (refresh/sync).
2. Feather/pen or lightning bolt for speed: a lightning bolt or a "fast" icon — maybe a stopwatch or a pen nib. Let me do a feather pen... simpler: a lightning bolt inside a circle? Keep it: a lightning bolt path.
3. Lock/shield for privacy: a shield with a check, or a padlock.

Feature copy (two sentences each):
1. "Sync before you blink" — "Start a thought on your phone, finish it at your desk — Nimbus keeps every device on the same page in under a second. No refresh button, no conflicts, no 'which copy is newest?'"
2. "Fast enough to keep up" — "Nimbus opens in a blink and captures keystrokes the moment they land, even on years-old hardware. When your tool is slower than your thinking, you lose the idea — we built it so you never do."
3. "Private by default" — "Every note is encrypted on your device before it ever leaves it, and only your devices hold the keys. We can't read your notes, and neither can anyone else."

Pricing:
- Free — $0 — "For personal notes that live on one or two devices." Bullets: 200 notes, sync across 2 devices, 7-day version history, community support. Button: "Start for free".
- Pro — $8/month — recommended. "For people who think in notes." Bullets: unlimited notes, sync across unlimited devices, unlimited version history, priority support + offline mode? Let me make the bullets: unlimited notes, sync across all your devices, full version history, priority support. Button: "Go Pro".
- Team — $20/month — "For teams that share a second brain." Bullets: everything in Pro, shared notebooks, real-time co-editing, admin controls & SSO? Keep: everything in Pro, shared team notebooks, real-time co-editing, admin controls & SSO. Button: "Start team trial".

Recommended tier: visually marked — a "Most popular" badge, a blue border/ring, slightly elevated/scaled on desktop, filled primary button vs. outline for others.

Footer: copyright line + 3 links (Privacy, Terms, Contact). Copyright: "© 2026 Nimbus Notes, Inc." Three links: Privacy, Terms, Support/Contact.

Accessibility details:
- Landmarks: header (top bar), nav (inside header), main, footer.
- Exactly one h1 (hero heading). Section headings are h2, feature titles and tier names are h3.
- Buttons: real <button> or <a>? CTA buttons that don't go anywhere — use <button type="button"> for CTAs (they're demo actions). Maybe show a small toast on click? "Interactive" is mostly about scroll + hover/focus. A toast on CTA click would be a nice touch: "This is a demo — Nimbus is imaginary. But your notes would be safe." Keep it subtle. Let me add a small toast for CTA clicks. That adds fun without bloat. Keep it accessible (role="status" aria-live="polite").
- Focus states: visible outline (2-3px) with offset; :focus-visible.
- Skip link? Good for a11y: "Skip to content." Add it — cheap and good practice.
- Contrast: all body text passes AA (checked above). Button text: white on #2E5BE6 ≈ 5.5:1, fine. Secondary link color #2E5BE6 on white ≈ 5.5:1, fine. Muted text #45536E on white ~6.5:1, fine. On the sky tint #E8F0FE, ink text is fine; muted on sky: #45536E vs #E8F0FE — luminance of E8F0FE is high (~0.86?), contrast ≈ (0.86+0.05)/(0.1006+0.05)... let me estimate luminance of #E8F0FE: r=232/255=0.9098→((0.9648)/1.055)=0.9145^2.4: ln≈-0.0894*2.4=-0.2145, e≈0.807. g=240/255=0.9412→(0.9962/1.055)=0.9443^2.4: ln≈-0.0573*2.4=-0.1375, e≈0.8715. b=254/255≈0.996→(1.051/1.055)=0.9962^2.4≈0.9909. L=0.2126*0.807+0.7152*0.8715+0.0722*0.9909=0.1716+0.6233+0.0715=0.8664. Contrast with #45536E (L=0.1006): (0.8664+0.05)/(0.1006+0.05)=0.9164/0.1506≈6.08. Fine.

- Pricing "recommended" badge: white text on blue, fine.
- Muted text on the mist background #F5F8FD: luminance of F5F8FD ≈ ? r=245→0.9608^... roughly L≈0.93. Contrast with #45536E: (0.93+0.05)/0.1506 ≈ 6.5. Fine.

Sticky top bar: position: sticky; top: 0; z-index. Add a shadow on scroll via a JS class (IntersectionObserver or a scroll listener). Keep it subtle.

Responsive:
- Container max-width: 1080px (or 1120), padding-inline: clamp.
- Hero: 2-column grid at ≥900px (copy left, visual right), stacked below.
- Features: 3-column grid → 1 column below 760px (or 3→1; maybe 3→2→1; with exactly 3 features, 3→1 is fine; at intermediate widths 3 columns might be cramped at ~700px; let me switch to 1 column below 860px, or use auto-fit minmax). Let me do grid-template-columns: repeat(3, 1fr) → 1fr below 820px.
- Pricing: 3 columns → 1 column below 900px. On mobile, order: keep Free, Pro, Team order (don't reorder; simpler and more honest).
- Top bar: below 640px, hamburger.

Type scale usage:
- h1: clamp(2.25rem, 5vw+1rem, 3.4rem)? The requirement is "one type scale" — I should use fixed scale steps, but clamp for the hero is common. To be safe, define scale tokens and use them; the hero can use the largest token (3.05rem), which is fine at 375px (49px at 375 is a bit large for a long heading; "Your thoughts, everywhere." at 49px would wrap fine). Let me use clamp within the token: h1: clamp(2.441rem, 1.5rem + 3vw, 3.052rem) — that's still "one scale" (the clamp interpolates between scale steps). I think that's defensible and looks better. Actually, to be strict, I can define --text-4xl: clamp(2.441rem, 2.05rem + 1.9vw, 3.052rem). Fine.

Spacing tokens: --s-1: 0.25rem; --s-2: 0.5rem; --s-3: 0.75rem; --s-4: 1rem; --s-5: 1.5rem; --s-6: 2rem; --s-7: 3rem; --s-8: 4rem; --s-9: 6rem. Use consistently.

Radius tokens: --r-sm: 8px; --r-md: 12px; --r-lg: 16px; --r-full: 999px.

Now the files:
- index.html
- style.css
- app.js

Let me write the copy in full.

Hero:
- Eyebrow: "Note-taking, minus the friction" or a small badge "New: offline mode". Keep: eyebrow "Synced notes for every screen."
- h1: "Your thoughts, everywhere you are."
- Subhead (one sentence): "Nimbus Notes keeps every scribble, spec and grocery list in perfect sync across your phone, laptop and the web — so you can start an idea anywhere and finish it anywhere." One sentence. Good.
- Primary CTA: "Start writing — it's free"
- Secondary link: "See how sync works ↓" linking to #features. Or "See what's inside." Let me use "See the features" → #features.

Top bar links: Home (#top / #hero), Features (#features), Pricing (#pricing). Hmm "links to the three sections below" — hero, features, pricing. Good.

Wait, should "Home" scroll to the hero? The hero is essentially at the top. A "Home" link that scrolls to the top is fine.

Actually, maybe better: make the three sections Features, Pricing, and... the hero is the only other section. OK, going with Home/Features/Pricing.

Feature section heading: h2 "Built to disappear into your workflow" + a one-sentence lead? The spec says each feature has an icon, title, and two sentences. A section heading is fine. h2: "Three things we obsess over" — hmm. Let me do: h2 "Why Nimbus" is too plain. "Everything a note app should be" — let me write: h2 "Small app. Serious about the basics." with a short lead sentence (optional). Keep it minimal: just h2 + 3 cards.

Feature titles:
1. "Sync before you blink"
2. "Fast enough to keep up"
3. "Private by default"

Pricing h2: "Pricing that stays out of your way" + sub "Start free. Upgrade when your notes outgrow the box."

Tier details:
Free — $0 /forever — "For casual note-takers."
- Up to 200 notes
- Sync across 2 devices
- 7-day version history
- Community support
Button: "Start for free"

Pro — $8 /month — "For people who think in notes." (Most popular badge)
- Unlimited notes
- Sync across all your devices
- Full version history
- Priority support
Button: "Go Pro"

Team — $20 /month — "For teams with a shared brain."
- Everything in Pro
- Shared team notebooks
- Real-time co-editing
- Admin controls & SSO
Button: "Start a team trial"

Note: "Team at $20/month" — per person per month? Just say $20/month as specified.

Footer: "© 2026 Nimbus Notes, Inc. All rights reserved." + links: Privacy, Terms, Contact. Maybe a small tagline too. Keep: left the copyright, right the links (stacked on mobile).

Now the hero SVG. Let me design it carefully.

viewBox="0 0 640 520". Elements:

1. A soft background cloud/blob: a large rounded shape behind, fill #E8F0FE (sky). Maybe two overlapping ellipses/rounded rectangles to form a cloud silhouette. Or a large soft circle. Let me do a cloud made of circles: a group of circles forming a cloud outline behind the devices, fill #E8F0FE.

2. A cloud icon at the top center: a white cloud with a blue sync arrow inside? Or a blue cloud with white sync arrows. Position at top center (~x 320, y 60). Cloud shape: a path or a combination of circles + rectangle. Let me draw a cloud path:
   Cloud path (classic): M ... use a known cloud path:
   `M25,60 a20,20 0 0,1 0-40 a25,25 0 0,1 48,-10 a22,22 0 0,1 27,21 a18,18 0 0,1 -5,29 z` — messy. Simpler: build the cloud from 3 circles + a rounded rectangle base, all with the same fill; overlaps are invisible with the same fill.
   - circle cx=290 cy=70 r=26
   - circle cx=320 cy=58 r=32
   - circle cx=352 cy=72 r=24
   - rect x=268 y=62 w=108 h=34 rx=17
   All fill white (or #fff), with a subtle stroke? A white cloud on the sky blob with a drop shadow looks nice. Inside the cloud: a blue sync arrow (two arcs with arrowheads).

   Sync arrow inside the cloud: two arcs: path1: M 305 78 a 15 15 0 0 1 26 -8 (arc from left to top-right) with an arrowhead at the end; path2 mirrored below. Let me define: center (320, 72), radius 14.
   - Top arc: M 306 72 A 14 14 0 0 1 334 72 → that's a semicircle from left to right passing over the top. Arrowhead at (334,72) pointing down-right: a small triangle polygon points "334,72 330,64 340,66"? Hmm, let me think: the arc ends at (334,72) moving downward (the direction of travel at the right end of an arc going over the top is downward). Arrowhead: a triangle pointing down at (334,72): points "328,66 340,66 334,76"? That points down. Good.
   - Bottom arc: M 334 72 A 14 14 0 0 1 306 72 (from right to left passing under the bottom). Arrowhead at (306,72) pointing up: triangle "300,78 312,78 306,68".
   Stroke #2E5BE6, width 3.5, fill none; arrowheads filled #2E5BE6.

3. Laptop: center-right. Body:
   - Screen outer: rect x=150 y=150 w=300 h=190 rx=12 fill #182642 (dark bezel)? Or a white laptop with a gray outline. Let me do: bezel fill #1E2C4E (dark navy), inner screen rect x=162 y=162 w=276 h=158 rx=6 fill #FFFFFF.
   - Base: a trapezoid below: path M120,340 L480,340 L500,362 Q500,370 490,370 L110,370 Q100,370 100,362 Z fill #D8E1F0? A simpler rounded rectangle: rect x=110 y=340 w=420 h=18 rx=9 fill #C9D6EC, with a notch rect x=290 y=340 w=60 h=6 rx=3 fill #AFC2E4.
   - Screen content (the app):
     - Title bar: rect x=162 y=162 w=276 h=26 rx=6 fill #E8F0FE (only top corners rounded — use a path, or overlay a rectangle to square off the bottom corners: simpler: a full rectangle with rx=6, then a small rect to square off the bottom of the bar). Or skip the title bar bar; use a window dot row: three circles at (176,175), (190,175), (204,175), r=4, fills #FF8A8A? No — keep the palette: use blue/gray dots: #F0B429? That introduces a new color. Keep palette: dots #C9D6EC, #C9D6EC, #2E5BE6? Hmm. Mac dots are usually red/yellow/green. My palette is small; I could use tinted dots: #AFC2E4 (pale), #7FA6F5 (mid), #2E5BE6 (deep). That stays in the blue family. Good.
     - Sidebar: rect x=162 y=188 w=88 h=132 fill #F5F8FD; sidebar items: 4 rounded rectangles (note rows): x=172, w=68, h=10, rx=5, y=200, 220, 240, 260; the active one fill #2E5BE6 (or #DCE7FB with a blue left bar). Let me make the active one fill #DCE7FB and a small blue dot.
     - Main note area: a title line: rect x=268 y=200 w=120 h=12 rx=6 fill #182642 (ink, representing the title text); text lines: rects w=150/140/150/90 h=8 rx=4 fill #C9D6EC, y=224, 240, 256, 272.
     - A "Synced" chip in the top-right of the screen: a rounded pill rect x=352 y=192 w=72 h=18 rx=9 fill #DCE7FB, with a small check circle + a small bar as text. Or a pill with a check icon: circle + polyline.

4. Phone: overlapping the laptop's bottom-right, in front.
   - Body: rect x=430 y=250 w=110 h=190 rx=18 fill #1E2C4E (navy bezel); screen rect x=438 y=258 w=94 h=174 rx=12 fill #FFFFFF.
   - Notch/speaker: rect x=470 y=264 w=30 h=5 rx=2.5 fill #C9D6EC? On white, use #D8E1F0.
   - Screen content: a title bar row: a small pill (back arrow?) keep: a title line

Empty directory. Let's make a plan:

1. `index.html` — semantic structure, inline SVG (logo, hero illustration, feature icons, checkmarks).
2. `style.css` — design tokens (type scale, spacing scale, palette), layout, responsive, hover/focus states.
3. `app.js` — mobile menu, scroll shadow, toast, year.

Let's write the files. Starting with index.html.

Next up is CSS. Design tokens:

Palette:
- --ink: #182642 (headings, dark)
- --ink-soft: #45536E (body text)
- --blue: #2E5BE6 (primary)
- --blue-deep: #1E3FAE (hover)
- --blue-soft: #7FA6F5
- --sky: #E8F0FE
- --sky-deep: #DCE7FB
- --line: #D8E1F0
- --paper: #FFFFFF
- --mist: #F5F8FD

Type scale (1.25 ratio):
--t-1: 0.8125rem (13)
--t-2: 0.9375rem (15)
--t-3: 1rem (16)
--t-4: 1.25rem (20)
--t-5: 1.5625rem (25)
--t-6: 1.953rem (31.25)
--t-7: 2.441rem (39)
--t-8: 3.052rem (48.83)

Spacing scale (rem, 4px base):
--s-1: .25, --s-2: .5, --s-3: .75, --s-4: 1, --s-5: 1.5, --s-6: 2, --s-7: 3, --s-8: 4, --s-9: 6

Layout: container max 1120px, padding-inline clamp(1rem, 4vw, 2rem).

Top bar: sticky, height 64px, white background, border-bottom is transparent → .is-scrolled adds border + shadow.

Nav: flex, gap; link is t-2 weight 600, color ink-soft; hover is blue; active? Skip.

Hero: padding block s-8/s-9; grid: at 900px and up, 1.05fr 1fr, gap s-8; align center. At 375px, stacked vertically with visual after copy.

Buttons:
.btn base: inline-flex, padding .75rem 1.25rem, radius 999, font t-3 weight 600, transition.
.btn--primary: bg blue, white text; hover bg blue-deep; focus-visible outline 3px blue offset 2.
.btn--ghost: bg white, border 1.5px line, color blue; hover: border blue, bg sky.
.text-link: color blue, weight 600, underline offset 3px; hover: color blue-deep, thicker underline.

Focus: global :focus-visible { outline: 3px solid var(--blue); outline-offset: 2px; border-radius inherit? } For links, outline works fine.

Skip link: absolute top-left, moves into view on focus.

Features: section bg is white (paper), top border? Use a subtle divider: features section is white, hero is mist. Pricing is mist? Let's alternate: hero (mist), features (white), pricing (sky-ish mist #F5F8FD), footer (ink dark? or white with top border). A dark footer looks more polished: footer bg is ink #182642, text is whitish. Contrast: #DCE7FB on #182642 is high. Links are #AFC2E4? Check contrast of #AFC2E4 on #182642: luminance of AFC2E4: r=175/255=0.686→((0.741)/1.055)=0.7024^2.4: ln≈-0.3532*2.4=-0.8477, e≈0.4284. g=194/255=0.7608→(0.8158/1.055)=0.7733^2.4: ln≈-0.2571*2.4=-0.617, e≈0.5395. b=228/255=0.8941→(0.9491/1.055)=0.8996^2.4: ln≈-0.1058*2.4=-0.2539, e≈0.7758. L=0.2126*0.4284+0.7152*0.5395+0.0722*0.7758=0.09108+0.38585+0.05601=0.53294. Luminance of ink #182642: r=24/255=0.0941→(0.1491/1.055)=0.1413^2.4: ln≈-1.957*2.4=-4.697, e≈0.00913. g=38/255=0.149→(0.204/1.055)=0.1934^2.4: ln≈-1.643*2.4=-3.943, e≈0.0194. b=66/255=0.2588→(0.3138/1.055)=0.2974^2.4: ln≈-1.2128*2.4=-2.9107, e≈0.0544. L=0.2126*0.00913+0.7152*0.0194+0.0722*0.0544=0.00194+0.013876+0.003928=0.019744. Contrast: (0.53294+0.05)/(0.019744+0.05)=0.58294/0.069744≈8.36.

Footer copyright text: #C9D6EC on ink — even higher. Good.

Footer link hover: white + underline.

Pricing cards: white bg, border 1px line, radius 16, padding s-6; featured: border 2px blue, badge, on desktop transform translateY(-8px) + shadow. Grid: 3 columns at 900px and up, gap s-5; below that, 1 column, max-width 480 centered? Just full width is fine.

Tier list: li with inline SVG check? I used plain li. Better: ::before checkmark. Use an inline SVG data URI as ::before background, or a CSS mask. Simplest: ::before content "✓"? Font checkmarks render inconsistently but are acceptable. Better: inline SVG data URI as ::before background. Let's do this: .tier__list li::before { content:""; width 18px height 18px, background url(data:image/svg+xml,...check in circle...) no-repeat center, margin-right .5rem }. Check SVG: circle fill #DCE7FB, check stroke #2E5BE6. Encode carefully.

SVG: <svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 20 20'><circle cx='10' cy='10' r='10' fill='%23DCE7FB'/><path d='M6 10.2l2.6 2.6 5.4-5.6' fill='none' stroke='%232E5BE6' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'/></svg>

URL-encode: # → %23, spaces are fine? In a data URI inside url("...") in CSS, spaces are OK if quoted. Encode # and keep the rest. Single quotes inside, double quotes on the outside.

Toast: fixed bottom center, bg ink, text white, padding, radius, opacity 0 translateY(8px), .is-visible → opacity 1 translateY(0), transition. z-index high.

Mobile menu:
@media (max-width: 640px):
- .menu-btn is display inline-flex.
- .nav { position: absolute; top: 100%; left:0; right:0; background white; border-bottom 1px line; box-shadow; display none; } .nav.is-open { display block; }
- .nav__list { flex-direction column; padding; gap; } links are block padding .75rem 1rem, border-radius.
Top bar is position sticky; nav is absolute relative to .topbar (topbar is position sticky → becomes containing block? sticky is positioned so absolute children anchor to it. Yes, sticky elements are positioned, so absolute children anchor to them.)

Desktop: .menu-btn is display none; .nav is static flex.

Reduced motion: @media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } * { transition-duration: 0.01ms !important; animation: none !important; } } Careful not to break toast visibility — toast uses opacity transition; with duration ~0 it just appears instantly. Fine.

html { scroll-behavior: smooth; scroll-padding-top: calc(topbar height + 16px); } Top bar height: 64px desktop, 56 mobile? Keep 64 fixed; scroll-padding-top: 80px.

Hero art: max-width 560px, width 100%, height auto.

Feature icons: 56px circle bg sky, svg 30px.

Section title: t-6 (1.953rem) at 375? 31px is fine. Desktop could be t-7 39px. Use clamp between t-6 and t-7: font-size: clamp(1.953rem, 1.5rem + 1.2vw, 2.441rem).

Eyebrow: t-2, uppercase, letter-spacing .08em, color blue, weight 700.

Hero title: clamp(2.441rem, 1.6rem + 2.6vw, 3.052rem), letter-spacing -0.02em, line-height 1.05.

Subhead: t-4 (1.25rem) ink-soft, line-height 1.55, max-width 46ch? At 375 that's fine.

Hero actions: flex wrap gap s-4, align center.

Container: width 100%, max-width 1120px, margin-inline auto, padding-inline clamp(1.25rem, 4vw, 2rem).

Now let's write style.css. Also add a subtle hover lift to feature cards. Feature card: white bg? Features section is white bg — cards need distinction: bg mist (#F5F8FD) with border line? Or keep section white with cards in sky tint. Let's do: features section bg white; cards bg #F5F8FD (mist) radius 16 padding s-6, hover: border color blue-soft + translateY(-4px) + shadow. Default border 1px line.

Pricing section bg: mist. Cards white. Featured card: white with blue border + shadow + badge.

Badge: inline-flex, bg blue, white text, t-1, uppercase? "Most popular" t-1 (13px) weight 700, padding .25rem .75rem, radius full, centered.

Tier name t-5 (1.5625rem) ink; tagline t-2 ink-soft; price amount t-7 ink, period t-2 ink-soft.

Tier list: t-3 ink-soft, line-height 1.5, li margin-bottom s-2, display flex align center gap .5rem.

Tier button: width 100%.

Footer: bg ink; inner flex space-between align center, wrap, gap; copyright t-2 #C9D6EC; links t-2 #AFC2E4 hover white underline.

Top bar inner: flex align center justify space-between, height 64px. Nav list: flex gap s-5 (20px) or 2rem. Nav link: t-2 weight 600 color ink-soft; hover color blue + underline? Use background-clip underline effect: text-underline-offset 4px, decoration thickness 2px.

Brand: flex gap .5rem align center; name t-4 (1.25rem) weight 700 ink, letter-spacing -0.01em.

Menu button: hidden on desktop. Style: border 1px line radius 8 padding .4rem .7rem, bg white, color ink, font t-2 weight 600, flex gap .4rem.

Toast: max-width min(92vw, 420px), text-align center.

Also add ::selection color sky.

One more consideration: "no horizontal scroll at any width" — ensure svg width 100% max-width, no fixed widths. Also, the hero grid's visual on mobile: art max-width 480px margin auto.

Let's write it.

Next, app.js: mobile menu toggle, top bar scroll shadow, toast on CTA click.

Alright, let me verify: read the files back and check for completeness/consistency. Also, do a quick sanity check on the contrast values and HTML validity. Let me re-read index.html to double-check a few points:

1. The `data-toast` attribute containing `’` HTML entities — when reading via getAttribute, the browser returns the decoded character ('). Good.

2. The footer copyright gets replaced by JS — no problem, the initial content is "© 2026" and JS updates it to the current year (2026). Consistent.

3. Check: the `.nav` inside `.topbar` — on mobile, `.nav` is `position: absolute; top: 100%`. `.topbar` is `position: sticky` — since sticky is a positioned element, absolute children are positioned relative to it. Good.

4. Potential issue: on desktop, `.nav` is a normal flex child of `.topbar__inner` (flex). `.nav__list` is flex. Good.

5. Hero grid on mobile: single column; visual comes after copy. Good.

6. `scroll-padding-top` uses --topbar-h, which changes at 640px. Good.

7. One concern: `.tier--featured` has `transform: translateY(-16px)` at ≥900px — the badge is positioned at top: -13px relative to the card; no problem.

8. `max-width: 560px; margin-inline: auto` on `.features__grid` and `.pricing__grid` at ≤900px — the cards are centered. Good.

9. `li::before` using a data URI — check the encoding: `%3Csvg...` with single quotes inside, wrapped in double quotes in CSS. Good.

10. Check the hero art: the sync arrow arcs — `M306 74 A 15 15 0 0 1 336 74` — from (306,74) to (336,74), radius 15, sweep 1 → the arc goes over the top (sweep=1 is clockwise; from left to right clockwise passes over the top). Chord length 30 = 2r, so it's a semicircle. Good. The second one: `M336 74 A 15 15 0 0 1 306 74` — from right to left, sweep 1 (clockwise) → passes under the bottom. Good. Arrowheads: top arc ends at (336,74) moving downward → downward-pointing triangle at (336,74): points "330,66 344,66 336,80" — a downward triangle with apex at (336,80). Slightly overlaps the arc's endpoint, but that's fine. Bottom arc ends at (306,74) moving upward → upward triangle: "300,82 314,82 306,68" — apex at (306,68). Good.

Wait, the cloud circles: circle cx=324 cy=54 r=33 → top edge is y=21; the rect is y=58 h=36 → bottom edge is 94. The arrows are centered at y=74, radius 15 → range y 59–89, x 306–336. Inside the cloud body (rect x 268–380, y 58–94, plus the circles). The top of the upper arc is y=59, right at the top edge of the rect — inside the circle region? At x=321, the top of the circle cy=54 r=33 is y=21, so y=59 is well inside. Good, the arrows fit within the cloud.

11. The dashed path from the phone to the cloud: `M488 244 C 452 180, 404 118, 356 90` — starts at (488,244), just above the top-right corner of the phone (phone top y=252, x 432–544). Good. Ends near the right side of the cloud (356,90) — the cloud's right circle is cx=356 cy=68 r=25 → bottom edge is y=93. Good.

12. Laptop screen: the sidebar rect is x=162 y=188 w=90 h=132 → bottom edge is 320, screen bottom edge is 162+158=320. Good. Main note area: title is x=268 (sidebar ends at 252). Lines are x=268 w=150 → ends at 418, screen right edge is 438. Good. Sync chip is x=350 w=76 → ends at 426 < 438. Good.

13. Phone screen: x=440–536, y=260–436. Content: title x=452 w=72 → 524 < 536. Lines are fine. Chip y=372 h=19 → 391. Screen bottom edge is 436, no problem.

14. Phone's bezel rect y=252 h=192 → bottom edge is 444. Screen y=260 h=176 → 436. Good.

15. Background ellipse: cx=320 cy=270 rx=295 ry=215 → x range 25–615, y range 55–485. viewBox is 640x520. Fits.

16. Check the laptop base path: `M112 342 L488 342 L502 362 Q 504 370 494 370 L106 370 Q 96 370 98 362 Z` — starts at (112,342), top edge to (488,342), right slant to (502,362), curve to (494,370), bottom edge to (106,370), curve to (98,362), close to (112,342). Good trapezoid.

17. Laptop screen outer frame: x=150 w=300 → 150–450. Base is 98–504. Good.

18. In the HTML, the `hero__art` svg has `role="img"` + title/desc with aria-labelledby. Good.

19. One h1 — yes. Heading order: h1 → h2 (features) → h3 ×3 → h2 (pricing) → h3 ×3. Good.

20. Landmarks: header, nav (primary), main, footer, nav (footer). Good.

21. Contrast checks (calculated earlier):
- ink-soft #45536e on white ≈ 6.9:1 ✓; on mist #F5F8FD ≈ 6.4:1 ✓; on sky #E8F0FE ≈ 6:1 ✓.
- blue #2E5BE6 on white ≈ 5.5:1 ✓ (links, ghost button text).
- White on blue ≈ 5.5:1 ✓ (primary button, badge).
- White on ink (toast, skip link) ≈ 13:1 ✓.
- Footer: #c9d6ec on #182642: L(c9d6ec): r=201/255=0.788→(0.843/1.055)=0.799^2.4: ln≈-0.2242*2.4=-0.538, e≈0.584. g=214/255=0.839→(0.894/1.055)=0.8474^2.4: ln≈-0.1657*2.4=-0.3977, e≈0.6718. b=236/255=0.9255→(0.9805/1.055)=0.9294^2.4: ln≈-0.0732*2.4=-0.1757, e≈0.8389. L=0.2126*0.584+0.7152*0.6718+0.0722*0.8389=0.12416+0.48047+0.06057=0.6652. Contrast: (0.6652+0.05)/(0.019744+0.05)=0.7152/0.069744≈10.25 ✓.
- #afc2e4 on ink ≈ 8.4 ✓.
- eyebrow blue on mist: L(mist)≈? F5F8FD: r=245→0.9608^... roughly L≈0.935. (0.935+0.05)/(0.1417+0.05)=0.985/0.1917≈5.14 ✓.
- tier__period ink-soft on white ✓.
- nav links ink-soft on white ✓.

22. "Exactly 3 features" ✓. "Each tier lists 4 bullet points" ✓ (4 each). "Each has its own button" ✓.

23. Top bar links to 3 sections: Home (#top), Features (#features), Pricing (#pricing) ✓.

24. Smooth scroll: CSS scroll-behavior + scroll-padding-top ✓.

25. No external resources: font is system, favicon is a data URI, check icon is a data URI. ✓

26. No horizontal scroll: all widths are fluid; the hero art has max-width; the container is fluid. The toast is max-width min(92vw,440px) ✓.

One more thing: the `.hero` background radial-gradient — `52rem 30rem at 85% -10%` is fine.

Also, the `.brand:hover .brand__mark` transform and the `.brand__mark` transition are defined in two separate blocks — the transition is declared after the hover rule, but CSS order doesn't matter for different properties. No problem.

Potential issue: `backdrop-filter` on the top bar over the hero — no problem.

The `menu-btn` label "Menu" + icon. aria-expanded on the button, aria-controls="site-nav" ✓.

Edge case: the outside-click handler on `document` also fires on menu button clicks (bubbling) — but menuBtn is inside topbar, so `topbar.contains(event.target)` is true → won't close. The menuBtn's own click handler toggles. Order: the button's click handler runs first (target phase), then the document handler — since the target is inside topbar, no double toggle. ✓

Escape: closes and focuses the button ✓.

Resize: closes if open above 640 ✓.

Now, let me verify the files were written completely — read them back. Also, if a headless browser is available, do a quick render test? Probably not available. At the very least, I can do a quick HTML parse check with python (html.parser) to detect tag mismatches. Let me do that.

The HTML is well-formed: 1 h1, 2 h2s, 6 h3s (3 features + 3 tiers), all landmarks present, 21 li's (3 nav + 3 features + 12 pricing + 3 footer = 21 ✓).

A few improvements to consider:

1. The `section` elements use `aria-labelledby` — no problem.
2. The hero art's `desc` element — in HTML5 inline SVG, `<desc>` is valid.
3. One issue: in the mobile nav, the `nav` element is `position: absolute` relative to `.topbar`. `.topbar` is `position: sticky` — good, since it's a positioned element.

But wait — there's a subtle issue: the `.nav` on desktop is a flex child of `.topbar__inner` (which is `display: flex`). `.nav` itself is a block containing `ul.nav__list` (flex). No problem.

4. `scroll-padding-top` — good for the sticky header offset.

5. Check: the top bar's `backdrop-filter` and `rgba` background — no problem.

6. Potential issue: `.tier--featured` has `transform: translateY(-16px)` at ≥900px, and the badge is at `top: -13px`. When the card moves up, could the badge get clipped? No, there's no overflow hidden. OK.

7. The `.hero__title`'s `max-width: 14ch` — "Your thoughts, everywhere you are." — at 14ch it might wrap awkwardly. Let me think: at 49px font, 14ch ≈ 14 * 0.5em ≈ 7em ≈ 343px. The container column at 1280 is about 500px. "Your thoughts," (14 chars including comma+space) fits on line 1, "everywhere you are." on line 2. Actually, that's a nice 2-line break. Hmm, "Your thoughts," = 14 chars → exactly 14ch. It might fit or might not depending on the font; either way it's fine.

8. Contrast re-check for `.tier__period` (#45536e on white) — 6.9:1 ✓.

9. `--blue-soft` #7fa6f5 is used for the dashed path in the SVG (decorative, so no problem).

10. One concern: the `:focus-visible` rule sets `border-radius: var(--r-sm)` on all focused elements — this overrides the border-radius of focused elements (e.g., a button with a full pill shape will show a focus outline with 8px radius — the outline follows the element's border-radius… actually, outline follows the element's border-radius. Setting border-radius in the focus rule would change the button's shape on focus! This is a bug: `.btn` has `border-radius: 999px`, but `:focus-visible` sets `border-radius: 8px`, so a focused button would appear as a rounded rectangle instead of a pill.

I should remove `border-radius` from the global `:focus-visible` rule. The outline will naturally follow the element's own radius.

11. Also, `.skip-link:focus-visible` sets `outline-color: var(--blue-soft)` — a blue-soft outline on a dark ink background: contrast of #7fa6f5 vs #182642 — L(#7fa6f5): r=127/255=0.498→(0.553/1.055)=0.5242^2.4: ln≈-0.6456*2.4=-1.549, e≈0.2125. g=166/255=0.651→(0.706/1.055)=0.6692^2.4: ln≈-0.4018*2.4=-0.964, e≈0.3813. b=245/255=0.9608→(1.0158/1.055)=0.9628^2.4: ln≈-0.0379*2.4=-0.091, e≈0.913. L=0.2126*0.2125+0.7152*0.3813+0.0722*0.913=0.04518+0.27271+0.06592=0.38381. Vs ink 0.019744: (0.38381+0.05)/(0.019744+0.05)=0.43381/0.069744≈6.2 ✓.

12. The toast is `pointer-events: none` — good.

13. In `app.js`, `el.getAttribute("data-toast")` returns the decoded text (with the ’ character). Good.

14. Check the `resize` listener — no problem.

15. Mobile: `.hero__actions` — the button + text link wrap. Good.

16. At 375px: top bar = brand (30px icon + "Nimbus Notes" 20px font ≈ 110px) + menu button (≈110px). Total ≈ 30+12+110+16+110+padding 40 ≈ 318 < 375 ✓.

17. `scroll-padding-top: calc(64px + 16px)` — good.

18. Another check: the `menu-btn` is `display: none` on desktop; in the DOM it's placed between brand and nav. In the flex row: brand, (hidden button), nav → space-between puts brand on the left and nav on the right. Good.

19. The `--topbar-h` variable is used for the top bar height and scroll-padding; on mobile it's 56px — `.topbar__inner` uses `height: var(--topbar-h)`, so it updates. Good.

20. The `.nav` dropdown on mobile: `top: 100%` is relative to `.topbar` (sticky). ✓

21. The `feDropShadow` filter on the group — supported in all modern browsers. ✓

22. `aria-hidden="true"` on the decorative feature icon span ✓.

23. The `li` in `features__grid` is a semantic list — no problem.

Now, let me fix the focus-visible border-radius issue. Also, I want to double-check the `:focus-visible` outline on the `.btn--primary` (blue button on white background): a blue outline on a blue button is somewhat low contrast, but the outline is drawn on the outside of the button, over the white page background → a blue outline on a white background is visible. OK.

Also, a minor improvement: the global `:focus-visible` sets `border-radius: var(--r-sm)` — remove it.

Let me also verify there are no other CSS issues. Re-checking the `.hero` background: `radial-gradient(52rem 30rem at 85% -10%, ...)` — a valid syntax (size position). ✓

`.tier__badge`'s `top: calc(-1 * var(--s-3) - 1px)` → -13px. ✓

One more: the `@media (max-width: 900px)` block sets `max-width: 560px; margin-inline: auto` on `.features__grid, .pricing__grid` — good for tablet/mobile.

Also, the `li::before` check icon data URI — verify the encoding is correct: `%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 20 20'%3E%3Ccircle cx='10' cy='10' r='10' fill='%23DCE7FB'/%3E%3Cpath d='M6 10.2l2.6 2.6 5.4-5.6' fill='none' stroke='%232E5BE6' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E` — inside a double-quoted url("..."), it's wrapped in single quotes. ✓

Also, verify that the favicon data URI in the HTML works: single quotes inside a double-quoted href. ✓

If possible, I'd like to do a quick visual sanity render with a headless browser. Check whether chromium/node/puppeteer is available. Probably not, but let me check quickly. If not, I'll rely on careful review.

Actually, let me first fix the CSS issue, then check for a headless browser for a screenshot test.

Chromium is available. I'll take screenshots at 1280px and 375px to verify the design, and check for horizontal scrolling and console errors.

I need to investigate this further. Let me check the details.

The screenshot has been captured. Let me display it to check the design.

In this environment I can't view images directly. Instead, I'll verify programmatically:

1. Check for horizontal overflow at 375px and 1280px (compare document.scrollWidth and innerWidth).
2. Check for console errors.
3. Verify that the main elements are rendered (e.g., computed styles, element positions).

I'll use Chromium's headless mode with --dump-dom, or better yet, use a small script with --headless --repl? A simpler approach: use `--headless=new --dump-dom` with a small inline script? Chromium headless screenshots can't execute custom JS.

Options: use Node with puppeteer? Probably not installed. Let me check if puppeteer is available, or use Chromium's `--headless --virtual-time-budget` together with `--run-all-compositor-stages-before-draw`... Actually, the simplest thing is: write a small test page that loads the same CSS/JS? No—better to verify with Chromium's `--headless --dump-dom`—but that only gives you the post-DOM-parse output, not the layout.

Alternative: use `--headless --screenshot` at different widths and analyze the PNG pixels programmatically (e.g., check whether the rightmost column has content)—but that's a hassle.

A better way: check if puppeteer-core is available in Node (can drive the system Chromium). Let me check the npm global packages.

No puppeteer. However, Chromium headless supports `--dump-dom`, and more usefully, it can execute JS via `--headless --repl`? Unreliable.

Alternative: Chromium headless supports `--print-to-pdf` and `--screenshot`. For layout verification, I could inject a small test harness: create a temporary copy of the page (test-only, don't ship) that adds a script at the end, writes the layout metrics into the DOM (e.g., sets document.title or adds a pre element), and then use `--dump-dom` to read it out. `--dump-dom` serializes the DOM after page load (with `--virtual-time-budget` to let JS run).

Let me try: copy index.html to /tmp/nimbus-test.html, but the relative links to style.css/app.js will break — either copy all 3 files to /tmp, or use file:// absolute paths. Easiest: create /tmp/nimbus-test/ with copies of the 3 files, and append a metrics script to the test copy of index.html.

Metrics script:
```js
window.addEventListener('load', () => {
  const m = {
    scrollWidth: document.documentElement.scrollWidth,
    innerWidth: window.innerWidth,
    bodyScrollWidth: document.body.scrollWidth,
    topbarHeight: document.querySelector('.topbar').getBoundingClientRect().height,
    h1: document.querySelector('h1').getBoundingClientRect().width,
    heroArt: document.querySelector('.hero__art').getBoundingClientRect(),
    ...
  };
  const pre = document.createElement('pre');
  pre.id = 'metrics';
  pre.textContent = JSON.stringify(m, null, 2);
  document.body.appendChild(pre);
});
```
Then run `chromium --headless --no-sandbox --window-size=375,800 --virtual-time-budget=3000 --dump-dom file:///tmp/nimbus-test/index.html | grep -A 40 'metrics'`.

Note: with --dump-dom and virtual-time-budget, the load event should fire and the script should run.

Check items:
- At 375: scrollWidth == 375 (no horizontal overflow)
- At 1280: scrollWidth == 1280
- Top bar height is 56 on mobile / 64 on desktop
- Menu button is visible on mobile (offsetParent is not null), hidden on desktop
- Nav is hidden on mobile (display none)

Also check for console errors: use `--enable-logging --v=1`? Console messages show up in stderr with `--enable-logging=stderr --v=0`. Let me capture stderr and grep for "ERROR" or "Uncaught".

OK, let's run it.

Wait a sec — the probe's `<script>` contains `</body>` inside the replacement string... no, that's not right, I replaced `</body>` with the probe + `</body>`. But the probe's script tag contains the string `</script>`, which terminates the script — that's fine, that's the actual terminator. However, the probe contains `</body>` inside the Python string, but not inside the JS. OK, good.

But there's one problem: the probe's script is placed before the actual `</body>`, and the original page's `<script src="app.js"></script>` is before that. The load event fires after app.js has executed. Good.

Next, run dump-dom at both widths.

Interesting — the window-size request is 375 but `innerWidth` is 500. Headless Chromium has a minimum window width (in old headless the minimum is around 500? Actually, in the newer version the minimum inner width for headless screenshots is 500). `--window-size=375,900` got clamped to 500. scrollWidth 485 < 500 → no overflow at 500. But I need to verify at an actual 375.

Options:
- Use `--force-device-scale-factor=1` + `--window-size=375` — got clamped.
- Use CDP directly: launch chromium with `--remote-debugging-port` and drive it with a small Node script using raw WebSocket… no, there's no ws library. But I can use Node 26's built-in WebSocket (Node 22+ has global WebSocket). I can talk to CDP via WebSocket from Node without any dependencies!

Plan:
1. Launch chromium headless with --remote-debugging-port=9222.
2. Node script: fetch http://127.0.0.1:9222/json/new?file:///... to create a tab (or use /json/list), connect to the WebSocket, and send Page.navigate, Emulation.setDeviceMetricsOverride {width:375, height:800, deviceScaleFactor:1, mobile:true}, wait for load, then Runtime.evaluate to grab metrics, and also capture console errors via Runtime.consoleAPICalled / Log.entryAdded.

This will give me a true 375px viewport. Let me write this.

Also, at 1280: innerWidth 1265 (15px scrollbar? Headless with --hide-scrollbars… without hide-scrollbars there's a 15px scrollbar). scrollWidth 1265 == innerWidth → no overflow. Good.

At 500 (mobile breakpoint ≤640): menuBtn visible, nav hidden, topbar height 57 (56 + 1 border). No overflow.

Also, at 768: heroArt width 560 — the art is centered in the single-column layout. features/pricing grids are 560 wide and centered. Good.

At 1280: heroArt w=484 (constrained by the grid column), h1 w=380 (max-width 14ch). featuredTier x=465 — the middle card. Good.

Note: at 1280, `heroArt` y=142 vs h1 y=168 — the art is vertically centered in the grid. No problem.

Now, let me do the CDP test at 375, and also capture console errors. I'll write the Node script.