# DESIGN.md: Arc-style design system

Measured from https://arc.net/ on 2026-10-14 by PikSpec (https://www.pikspec.com). An independent measurement of the rendered page, not Arc's official design system, and not affiliated with Arc.

Use it to build your own product in this design language: put this file in your project root and tell your AI tool (Claude Code, Cursor, Codex, Lovable, v0) to follow DESIGN.md. Never use the original's name, logo, copy or images; licensed fonts are replaced with the closest free Google Fonts.

To capture any other page, or get a ready project for your tool: https://www.pikspec.com/build-with-ai

HOW IT SHOULD LOOK
Build it in the design language of arc.net, measured from the live site: it should feel designed by the same team as arc.net — the same temperament, colour, type and density — for a different product. Never use arc.net's name, logo, words or images.

Stack: use the one your project already has. Starting fresh: React + Vite + TypeScript + Tailwind CSS v4, with no UI kit (no shadcn/ui, MUI or Chakra) — their defaults would override this system. In a chat that shows one file (an artifact or canvas), build one HTML file instead, with the tokens below in its <style> block.
Use every value exactly as written. Do not round, rename, approximate or substitute a colour, size, radius, shadow or easing (fonts: see section 1). Anything not listed here does not exist in this system.

THE WEBSITE THIS SYSTEM COMES FROM
- Reference page: https://arc.net/ — "arc.net" (home page).
- Page frame: a top navigation bar and a footer.
- It uses 16 images including 2 videos, 13 of them large. Large, real product imagery is part of the look — leave clearly labelled image slots at those sizes rather than stock photos or abstract 3D shapes.
- Interaction: 5 buttons on one page.
- The page runs about 7 screens long at 1440px wide.
- Density is low: few elements per screen, generous space around each one.

HOW IT LOOKS (WHAT MAKES IT LOOK LIKE ITSELF, BEYOND THE VALUES)
- Mostly neutral: 86% of the page is #FFFCEC and #FFFFFF and other neutrals; #3139FB (13.8%) fills whole sections.
- #2702C2 is an accent: 0.1% of the page, as small fills such as buttons and badges. Keep it to small areas.
- The largest type (45.51px Marlin Soft SQ) is bold (700), tracked to -0.04em.
- Open: text covers 6% of the page. Sections sit about 103px apart.
- Share of the painted page: #FFFCEC 56.7% (dominant, backgrounds); #FFFFFF 28.5% (dominant, backgrounds); #3139FB 13.8% (supporting, backgrounds and text); #000000 0.5% (detail, backgrounds and text); #696969 0.3% (detail, text); #2702C2 0.1% (accent, backgrounds and text); #FFFADD 0.1% (detail, text). Keep accents at these proportions; do not promote them to fills.
- Large images: Photographs, video or raster artwork cover about 116% of the page.
- Type as set (size, weight and tracking measured together; use these pairs): 45.51px weight 700 tracking -0.04em; 40px weight 700 tracking -0.04em; 36px weight 700 tracking -0.02em; 28px weight 700 tracking -0.05em; 24px weight 400; 20px weight 400.

1. DESIGN TOKENS — PASTE INTO YOUR GLOBAL CSS
Allowed colours, with how the original uses each. Use no other colour, including in hover states:
- #FFFCEC — 56.7% · backgrounds (var(--color-surface))
- #FFFFFF — 28.5% · backgrounds (var(--color-background))
- #3139FB — 13.8% · backgrounds, text (var(--color-text))
- #000000 — 0.5% · backgrounds, text (var(--color-000000))
- #696969 — 0.3% · text
- #2702C2 — 0.1% · backgrounds, text
- #FFFADD — 0.1% · text
Fonts — put these first in your global CSS (one import per font, so one that fails cannot stop the others):
```css
@import url("https://fonts.googleapis.com/css2?family=Figtree:wght@500;700&display=swap");
@import url("https://fonts.googleapis.com/css2?family=Inter:wght@500;600;700&display=swap");
@import url("https://fonts.googleapis.com/css2?family=JetBrains+Mono:wght@400;700&display=swap");
```
Font: arc.net uses Marlin Soft SQ (body) and ABC Favorit Mono (code) — its own licensed faces, not available to download. This kit uses Figtree for body and JetBrains Mono for code, the closest free matches, already in the tokens. If you own the original, add it with @font-face and it is used first; to use another font, change the --font-* variables.
InterVariable (Google's Inter) is on Google Fonts and loaded from there.
Keep every size, weight, line height and tracking exactly as listed whichever font renders.
```css
:root {
  --color-background: #FFFFFF; /* Background */
  --color-surface: #FFFCEC; /* Surface */
  --color-text: #3139FB; /* Text */
  --color-action: #3139FB; /* Action */
  --color-on-action: #FFFFFF; /* On action */
  --color-000000: #000000; /* 0.5% of the page, as fills */
  --font-body: "Marlin Soft SQ", "Figtree", sans-serif; /* Marlin Soft SQ on the site; Figtree renders */
  --font-interface: "InterVariable", "Inter", sans-serif; /* InterVariable on the site; Inter renders */
  --font-code: "ABC Favorit Mono", "JetBrains Mono", monospace; /* ABC Favorit Mono on the site; JetBrains Mono renders */
  --type-display-large: 45.51px; /* Display Large, weight 700 */
  --type-display-large-leading: 42.25px;
  --type-display-large-tracking: -0.04em;
  --type-display-medium: 40px; /* Display Medium, weight 700 */
  --type-display-medium-leading: 39px;
  --type-display-medium-tracking: -0.04em;
  --type-display-small: 36px; /* Display Small, weight 700 */
  --type-display-small-leading: 36px;
  --type-display-small-tracking: -0.02em;
  --type-headline-large: 28px; /* Headline Large, weight 700 */
  --type-headline-large-leading: 30px;
  --type-headline-large-tracking: -0.05em;
  --type-headline-small: 24px; /* Headline Small, weight 400 */
  --type-headline-small-leading: 28.8px;
  --type-title: 20px; /* Title, weight 400 */
  --type-title-leading: 24px;
  --type-body-large: 17px; /* Body Large, weight 500 */
  --type-body-large-leading: 25.5px;
  --type-body-medium: 16px; /* Body Medium, weight 700 */
  --type-body-medium-leading: normal;
  --type-body-small: 14px; /* Body Small, weight 600 */
  --type-body-small-leading: normal;
  --type-body-small-tracking: -0.01em;
  --type-label-large: 13px; /* Label Large, weight 400 */
  --type-label-large-leading: normal;
  --type-label-small: 12px; /* Label Small, weight 600 */
  --type-label-small-leading: normal;
  --type-label-small-tracking: 0.033em;
  --space-1: 4px;
  --space-2: 8px;
  --space-3: 12px;
  --space-4: 16px;
  --space-5: 20px;
  --space-6: 24px;
  --space-8: 32px;
  --space-10: 40px;
  --space-12: 48px;
  --space-18: 72px;
  --space-20: 80px;
  --space-25: 100px;
  --space-32: 128px;
  --space-42: 168px;
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 10px;
  --radius-2xl: 18px;
  --radius-3xl: 22px;
  --elevation-1: rgba(0, 0, 0, 0.1) 0px 5px 5px 0px;
  --elevation-2: rgba(0, 0, 0, 0.25) 0px 2px 8px 0px;
  --duration-1: 0.15s;
  --duration-2: 0.2s;
  --ease-1: ease-in-out;
  --ease-2: ease-out;
}
```
Tailwind CSS v4 (the default for new projects): put this after `@import "tailwindcss";`. It removes Tailwind's own palette, so only these colours exist as utilities:
```css
@theme {
  --color-*: initial;
  --color-background: #FFFFFF;
  --color-surface: #FFFCEC;
  --color-text: #3139FB;
  --color-action: #3139FB;
  --color-on-action: #FFFFFF;
  --color-000000: #000000;
  --font-body: "Marlin Soft SQ", "Figtree", sans-serif;
  --font-interface: "InterVariable", "Inter", sans-serif;
  --font-code: "ABC Favorit Mono", "JetBrains Mono", monospace;
  --text-display-large: 45.51px;
  --text-display-large--line-height: 42.25px;
  --text-display-large--letter-spacing: -0.04em;
  --text-display-medium: 40px;
  --text-display-medium--line-height: 39px;
  --text-display-medium--letter-spacing: -0.04em;
  --text-display-small: 36px;
  --text-display-small--line-height: 36px;
  --text-display-small--letter-spacing: -0.02em;
  --text-headline-large: 28px;
  --text-headline-large--line-height: 30px;
  --text-headline-large--letter-spacing: -0.05em;
  --text-headline-small: 24px;
  --text-headline-small--line-height: 28.8px;
  --text-title: 20px;
  --text-title--line-height: 24px;
  --text-body-large: 17px;
  --text-body-large--line-height: 25.5px;
  --text-body-medium: 16px;
  --text-body-small: 14px;
  --text-body-small--letter-spacing: -0.01em;
  --text-label-large: 13px;
  --text-label-small: 12px;
  --text-label-small--letter-spacing: 0.033em;
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 10px;
  --radius-2xl: 18px;
  --radius-3xl: 22px;
  --shadow-e1: rgba(0, 0, 0, 0.1) 0px 5px 5px 0px;
  --shadow-e2: rgba(0, 0, 0, 0.25) 0px 2px 8px 0px;
  --ease-1: ease-in-out;
  --ease-2: ease-out;
}
```
Tailwind CSS v3 only: extend the theme with these instead, and use no other palette:
```js
// tailwind.config — theme.extend
{
  colors: { "background": "var(--color-background)", "surface": "var(--color-surface)", "text": "var(--color-text)", "action": "var(--color-action)", "on-action": "var(--color-on-action)" },
  fontFamily: { "body": ["var(--font-body)"], "interface": ["var(--font-interface)"], "code": ["var(--font-code)"] },
  borderRadius: { "sm": "var(--radius-sm)", "md": "var(--radius-md)", "lg": "var(--radius-lg)", "2xl": "var(--radius-2xl)", "3xl": "var(--radius-3xl)" },
  boxShadow: { "e1": "var(--elevation-1)", "e2": "var(--elevation-2)" },
}
```

2. BASE STYLES
```css
html { background: var(--color-background); }
body { margin: 0; font-family: var(--font-body); font-size: var(--type-body-large); line-height: var(--type-body-large-leading); color: var(--color-text); -webkit-font-smoothing: antialiased; -moz-osx-font-smoothing: grayscale; }
h1, h2, h3 { font-family: var(--font-body); margin: 0; }
a { color: inherit; }
:focus-visible { outline: 2px solid var(--color-action); outline-offset: 2px; }
```

3. COMPONENTS — MATCH THESE EXACTLY
```css
.link { /* Strong */
  background: transparent;
  padding: var(--space-6);
  min-height: 69px;
  color: var(--color-text);
  font-family: var(--font-body);
  font-size: var(--type-body-medium);
  font-weight: 700;
  /* recorded states: focus-visible */
}
.link-2 { /* Strong 2 */
  background: transparent;
  border-radius: var(--radius-sm);
  color: var(--color-text);
  font-family: var(--font-interface);
  font-size: var(--type-body-large);
  font-weight: 700;
  line-height: 25.5px;
  /* recorded states: focus-visible, hover, focus */
}
.link-3 { /* Inline */
  background: transparent;
  min-height: 32px;
  color: var(--color-000000);
  font-family: "Marlin";
  font-size: var(--type-body-medium);
  font-weight: 400;
  /* recorded states: focus-visible */
}
.button { /* Primary */
  background: var(--color-action);
  border-radius: var(--radius-3xl);
  padding: 8px 22px 8px 8px;
  min-height: 76px;
  box-shadow: var(--elevation-2);
  color: var(--color-on-action);
  font-family: "ABC Oracle";
  font-size: var(--type-headline-small);
  font-weight: 400;
  line-height: 28.8px;
  /* recorded states: focus-visible, hover */
}
.button-2 { /* Secondary */
  background: var(--color-000000);
  border-radius: var(--radius-2xl);
  padding: 8px 22px 8px 8px;
  min-height: 58px;
  box-shadow: var(--elevation-2);
  color: #FFFFFF;
  font-family: "ABC Oracle";
  font-size: var(--type-title);
  font-weight: 400;
  line-height: 24px;
  /* recorded states: focus-visible, hover */
}
.button-3 { /* Secondary 2 */
  background: var(--color-background);
  border-radius: var(--radius-lg);
  padding: 8px 0px 8px 0px;
  min-height: 45px;
  box-shadow: var(--elevation-1);
  color: #2702C2;
  font-family: "-apple-system";
  font-size: var(--type-body-small);
  font-weight: 600;
  line-height: 29px;
  /* recorded states: focus-visible, hover, focus, active */
}
.nav { /* Default */
  background: transparent;
  min-height: 39px;
  color: var(--color-000000);
  font-family: "Marlin";
  font-size: var(--type-body-medium);
  font-weight: 400;
}
```
Where a component lists recorded states, write those states using only the colours above; the capture saw that the state exists, not its values. Never invent a state colour.

4. PAGE COMPOSITION
- Light interface on #FFFFFF. Keep that ground; do not add a dark mode.
- The opening screen carries a large image or video on the middle. Leave a [content: hero image or video] slot there, at least half the screen wide; the opening is not text alone.
- Sections change ground between Text (#3139FB) and Surface (#FFFCEC); use only those.
- #3139FB is the action colour. Fill the primary action with it and little else — at most one #3139FB-filled element per screen; other accents keep to the uses listed above.
- Type: Figtree (standing in for Marlin Soft SQ) for body; Inter for interface; JetBrains Mono (standing in for ABC Favorit Mono) for code. Hierarchy comes from size and weight, not colour or decoration.
- Everything sits on a 4px grid.
- Corner radii are 4px, 8px, 10px, 18px, 22px — nothing else.
- Body text uses Marlin Soft SQ at around 16px, weights 500, 700.
- Headings use Exposure VAR; the largest heading is 45.51px.
- Primary buttons are #3139FB, 22px radius, weight 400.
- Corner radii in use: 8px, 10px, 22px, 18px, 4px.

HOW THE ORIGINAL PACES ITS PAGE (BORROW THE RHYTHM — THE OPENING, THE COLOURED BANDS, THE CARD GRIDS — NOT THE LIST; BUILD THE SECTIONS YOUR PRODUCT NEEDS)
1. Hero — 617px tall, centred 36px heading (weight 700), image centred, on #FFFCEC.
2. Hero — 920px tall, centred 45.51px heading (weight 700), image behind the content, on #3139FB.
3. Split — 67px tall, 2 equal columns, left-aligned 16px heading (weight 700), image on the right, on #FFFCEC.
4. Full-bleed image — 1080px tall, centred 40px heading (weight 700), image behind the content.
5. Full-bleed image (×2) — 2 bands of 1041px, centred 40px heading (weight 700), image behind the content.
6. Statement — 140px tall, centred 40px heading (weight 700).
7. Cards — 373px tall, 4 equal columns, 16px gap, centred 28px heading (weight 700), on #FFFCEC.
8. Footer — 508px tall, centred 28px heading (weight 700), image behind the content, on #3139FB.
- The hero is 617px (0.7 screens): centred 36px heading (weight 700), image centred, on #FFFCEC.
- Column splits on a 12-column grid: halves, quarters; gaps of 16px.
- Headings are centred (7 of 8 sections).
- Sections change background 5 times, between #FFFCEC, #3139FB: colour comes in full-width bands, not in boxes.
- A typical section is about 373px tall.

COPY SHAPE (MATCH THE LENGTH AND CASE; WRITE YOUR OWN WORDS)
- The main heading is 9 words long.
- Section headings are long: typically 9 words.
- Headings are in sentence case (only the first word capitalised).
- The page describes itself in about 25 words; keep your intro paragraph to about that length.

5. MOTION
Interactive elements change colour, background, border and opacity with the measured timing. Animate nothing else.
```css
a, button, [role="button"], input { transition: color var(--duration-1) var(--ease-1), background-color var(--duration-1) var(--ease-1), border-color var(--duration-1) var(--ease-1), opacity var(--duration-1) var(--ease-1); }
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation-duration: 0.01ms !important; animation-iteration-count: 1 !important; transition-duration: 0.01ms !important; scroll-behavior: auto !important; }
}
```
No scroll-triggered fade-ins, parallax, typewriter text or bouncing elements.

6. RESPONSIVE
- The design was measured at 1440px wide. Lay it out for that width first, then let it reflow down to 360px.
- Content sits in a column at most 760px wide, centred, with var(--space-4) (16px) side padding on small screens.
- The largest heading scales fluidly: font-size: clamp(24px, 3.2vw, 45.51px). Every other size stays fixed.
- Break on composition, not device names: a row of columns drops a column when any column would be narrower than 240px; side-by-side splits stack when either side would be narrower than 320px.
- Spacing steps never change between sizes; use smaller steps from the same list where space is tight.
- On touch screens, every link and button has a hit area of at least 44 × 44px without changing its drawn size.

7. ACCESSIBILITY
- Text pairs that pass for body copy: Text on Background (6.8:1), Action on Background (6.8:1), Text on Surface (6.6:1), Action on Surface (6.6:1) and On action on Action (6.8:1).
- Use no other text-on-background pairing.
- One h1 per page, headings in order, landmarks (header, nav, main, footer), real buttons and links, a label on every field, alt text on every image, an aria-label on icon-only buttons.
- Every interactive element shows the :focus-visible outline above.

8. DO NOT (THESE ARE WHAT MAKE AI-BUILT SITES LOOK GENERIC)
- Only the two shadows in the tokens, on the components that use them. (2 shadow values were measured; inventing softer ones changes the depth of the page.)
- No gradients: not in backgrounds, text, buttons or borders. (No gradient was measured.)
- Only these colours: #FFFCEC, #FFFFFF, #3139FB, #000000, #696969, #2702C2, #FFFADD. No new tints, no Tailwind defaults (slate, indigo, violet). (They are every colour that covers a measurable part of the page, and the colours its lines and drawings use.)
- #2702C2 only as small fills (buttons, badges) — never a section background or a large panel. (It covers 0.1% of the page.)
- Only the fonts in the tokens: Figtree for body; Inter for interface; JetBrains Mono for code. No other typeface, and no Inter, Roboto or system UI font unless it is one of these. (The page is set in Marlin Soft SQ and InterVariable and Exposure VAR; the tokens carry what stands in for them.)
- Headings and large text never heavier than weight 700. Do not make headlines bold to add emphasis. (Every size from 24px up is set at weight 700 or lighter.)
- Large headlines tracked tight (letter-spacing -0.04em), not at the browser default. (The 45.51px headline is set at -0.04em.)
- No icon above every feature, no emoji, no decorative blobs, sparkles or glows. (None of these is part of the captured design; they are a coding model's defaults.)
- Build the sections your product needs, not the original's list. Give each one this system's look: its kinds of section (hero, split, image, statement, cards, footer), its colours, type, shapes and spacing. (The style carries to any kind of site; the original's page was for a different product.)
- No glassmorphism, backdrop blur, glowing orbs, noise blobs or neon outlines.
- No row of three identical feature cards as the default section. Vary the layout from section to section: a split, a list, a single large statement, a table.
- No centred-everything hero with a pill badge, a gradient headline and two buttons. Lead with the most specific thing about the product.
- No filler copy: no "Unlock your potential", "Revolutionize", "Seamless", "Elevate", "Supercharge", "Next-gen" or lorem ipsum. Write plain, specific sentences a real company would publish.
- No made-up statistics, testimonials or customer logos. Leave a clearly marked [content: …] slot instead.
- No radius larger than the largest one listed.
- Do not use arc.net's name, logo, copy or images. This is its design system, not its content.

BEFORE YOU FINISH
- Search your code for every colour, font size, spacing value, radius, shadow and easing, and replace anything that is not a variable above.
- Check that no [content: …] slot has been filled with invented facts.
- Search your CSS for gradient(. There should be none.
- Every colour value in your CSS is one of the allowed colours. Nothing else, including in hover states.
- #2702C2 covers about 0.1% of the page or less, as on the original.
- No text 24px or larger has a font-weight above 700.
- The largest headline uses letter-spacing -0.04em.
- Every section, including ones the original does not have, uses only this system's colours, type, shapes and spacing.
- Content sits in a 1400px container with the measuredpx side margins at 1440px.
- There is no placeholder copy (lorem ipsum, "Feature one", "Your headline here"). Every word is real.
- Take a screenshot at 1440px and put it beside the original. List every difference in colour, weight, spacing, alignment and imagery, and fix each before finishing. Then check 390px wide: nothing scrolls sideways and no heading runs off the screen.