# DESIGN.md: Mercury-style design system

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

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 mercury.com, measured from the live site: it should feel designed by the same team as mercury.com — the same temperament, colour, type and density — for a different product. Never use mercury.com'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://mercury.com/ — "mercury.com" (home page).
- Page frame: a top navigation bar and a footer.
- Content is grouped in cards (6 on the page). Keep cards for grouped content only, not for every section.
- It uses 199 images including 7 videos, 57 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: 34 buttons and 1 form field on one page.
- The page runs about 13 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)
- Almost entirely neutral: 99% of the page is painted in #171721 and #FFFFFF.
- #5266EB is an accent: under 0.1% of the page, as small fills such as buttons and badges. Keep it to small areas.
- #CDDDFF is an accent: under 0.1% of the page, as small fills such as buttons and badges. Keep it to small areas.
- The largest type (65.34px arcadiaDisplay) is medium weight, not bold (480).
- Very airy: text covers 4% of the page.
- Share of the painted page: #171721 56.8% (dominant, backgrounds); #FFFFFF 37.4% (dominant, backgrounds); #EDEDF3 2.5% (supporting, text); #1E1E2A 1.7% (detail, backgrounds); #C3C3CC 1.3% (supporting, text); #FCFCFA 0.2% (detail, backgrounds). Keep accents at these proportions; do not promote them to fills.
- Hairline dividers: 1px lines in #AFB2CE separate sections and rows (20 of them).
- Large images: Photographs, video or raster artwork cover about 28% of the page.
- Type as set (size, weight and tracking measured together; use these pairs): 65.34px weight 480; 49.35px weight 480; 42px weight 480 tracking 0.01em; 32px weight 480 tracking 0.015em; 28px weight 360 tracking 0.015em; 24px weight 480 tracking 0.02em.

1. DESIGN TOKENS — PASTE INTO YOUR GLOBAL CSS
Allowed colours, with how the original uses each. Use no other colour, including in hover states:
- #171721 — 56.8% · backgrounds (var(--color-background))
- #FFFFFF — 37.4% · backgrounds (var(--color-ffffff))
- #EDEDF3 — 2.5% · text (var(--color-text))
- #1E1E2A — 1.7% · backgrounds (var(--color-1e1e2a))
- #C3C3CC — 1.3% · text (var(--color-text-muted))
- #FCFCFA — 0.2% · backgrounds
- #70707D — hairlines and grid lines
- #2A2924 — small marks
- #272735 — Surface (var(--color-surface))
- #9CB4E8 — Action (var(--color-action))
- #000000 — On action (var(--color-on-action))
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@400;500;700&display=swap");
@import url("https://fonts.googleapis.com/css2?family=Archivo:wght@400;500&display=swap");
```
Font: mercury.com uses arcadia (body) and arcadiaDisplay (display) — its own licensed faces, not available to download. This kit uses Figtree for body and Archivo for display, 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.
Keep every size, weight, line height and tracking exactly as listed whichever font renders.
```css
:root {
  --color-background: #171721; /* Background */
  --color-surface: #272735; /* Surface */
  --color-text: #EDEDF3; /* Text */
  --color-text-muted: #C3C3CC; /* Text muted */
  --color-action: #9CB4E8; /* Action */
  --color-on-action: #000000; /* On action */
  --color-ffffff: #FFFFFF; /* 37.4% of the page, as fills */
  --color-1e1e2a: #1E1E2A; /* 1.7% of the page, as fills */
  --font-body: arcadia, "Figtree", sans-serif; /* arcadia on the site; Figtree renders */
  --font-display: "arcadiaDisplay", "Archivo", sans-serif; /* arcadiaDisplay on the site; Archivo renders */
  --type-display-large: 65.34px; /* Display Large, weight 480 */
  --type-display-large-leading: 71.8784px;
  --type-display-medium: 49.35px; /* Display Medium, weight 480 */
  --type-display-medium-leading: 54.2819px;
  --type-display-small: 42px; /* Display Small, weight 480 */
  --type-display-small-leading: 48.3px;
  --type-display-small-tracking: 0.01em;
  --type-headline-large: 32px; /* Headline Large, weight 480 */
  --type-headline-large-leading: 36.8px;
  --type-headline-large-tracking: 0.015em;
  --type-headline-medium: 28px; /* Headline Medium, weight 360 */
  --type-headline-medium-leading: 33.6px;
  --type-headline-medium-tracking: 0.015em;
  --type-headline-small: 24px; /* Headline Small, weight 480 */
  --type-headline-small-leading: 28.8px;
  --type-headline-small-tracking: 0.02em;
  --type-title-large: 21.01px; /* Title Large, weight 360 */
  --type-title-large-leading: 28.3608px;
  --type-title-small: 18px; /* Title Small, weight 360 */
  --type-title-small-leading: 24.3px;
  --type-body: 16px; /* Body, weight 400 */
  --type-body-leading: 22.4px;
  --type-label: 12px; /* Label, weight 400 */
  --type-label-leading: 16.8px;
  --type-label-tracking: 0.02em;
  --space-2: 8px;
  --space-4: 16px;
  --space-6: 24px;
  --space-8: 32px;
  --space-10: 40px;
  --space-14: 56px;
  --space-18: 72px;
  --space-20: 80px;
  --space-28: 112px;
  --space-32: 128px;
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --radius-3xl: 32px;
  --radius-full: 9999px;
  --radius-40: 40px; /* component radius */
  --elevation-1: rgba(0, 0, 0, 0) 0px 0px 0px 0px, rgba(0, 0, 0, 0) 0px 0px 0px 0px, rgba(0, 0, 0, 0) 0px 0px 0px 0px, rgba(0, 0, 0, 0) 0px 0px 0px 0px, rgba(28, 28, 35, 0.02) 0px 10px 16px 0px, rgba(28, 28, 35, 0.04) 0px 6px 10px 0px, rgba(28, 28, 35, 0.09) 0px 0px 3px 0px;
  --elevation-2: rgba(0, 0, 0, 0) 0px 0px 0px 0px, rgba(0, 0, 0, 0) 0px 0px 0px 0px, rgba(0, 0, 0, 0) 0px 0px 0px 0px, rgba(0, 0, 0, 0) 0px 0px 0px 0px, rgba(0, 0, 0, 0.05) 0px 0px 3px 0px, rgba(0, 0, 0, 0.05) 0px 8px 12px 0px, rgba(0, 0, 0, 0.05) 0px 12px 20px 0px;
  --duration-1: 0.15s;
  --duration-2: 0.2s;
  --duration-3: 0.3s;
  --duration-4: 0.5s;
  --duration-5: 0.6s;
  --ease-1: cubic-bezier(0, 0, 0.6, 1);
  --ease-2: cubic-bezier(0, 0, 0.2, 1);
  --ease-3: cubic-bezier(0.4, 0, 0.2, 1);
  --ease-4: cubic-bezier(0.76, 0, 0.24, 1);
}
```
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: #171721;
  --color-surface: #272735;
  --color-text: #EDEDF3;
  --color-text-muted: #C3C3CC;
  --color-action: #9CB4E8;
  --color-on-action: #000000;
  --color-ffffff: #FFFFFF;
  --color-1e1e2a: #1E1E2A;
  --font-body: arcadia, "Figtree", sans-serif;
  --font-display: "arcadiaDisplay", "Archivo", sans-serif;
  --text-display-large: 65.34px;
  --text-display-large--line-height: 71.8784px;
  --text-display-medium: 49.35px;
  --text-display-medium--line-height: 54.2819px;
  --text-display-small: 42px;
  --text-display-small--line-height: 48.3px;
  --text-display-small--letter-spacing: 0.01em;
  --text-headline-large: 32px;
  --text-headline-large--line-height: 36.8px;
  --text-headline-large--letter-spacing: 0.015em;
  --text-headline-medium: 28px;
  --text-headline-medium--line-height: 33.6px;
  --text-headline-medium--letter-spacing: 0.015em;
  --text-headline-small: 24px;
  --text-headline-small--line-height: 28.8px;
  --text-headline-small--letter-spacing: 0.02em;
  --text-title-large: 21.01px;
  --text-title-large--line-height: 28.3608px;
  --text-title-small: 18px;
  --text-title-small--line-height: 24.3px;
  --text-body: 16px;
  --text-body--line-height: 22.4px;
  --text-label: 12px;
  --text-label--line-height: 16.8px;
  --text-label--letter-spacing: 0.02em;
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --radius-3xl: 32px;
  --radius-full: 9999px;
  --shadow-e1: rgba(0, 0, 0, 0) 0px 0px 0px 0px, rgba(0, 0, 0, 0) 0px 0px 0px 0px, rgba(0, 0, 0, 0) 0px 0px 0px 0px, rgba(0, 0, 0, 0) 0px 0px 0px 0px, rgba(28, 28, 35, 0.02) 0px 10px 16px 0px, rgba(28, 28, 35, 0.04) 0px 6px 10px 0px, rgba(28, 28, 35, 0.09) 0px 0px 3px 0px;
  --shadow-e2: rgba(0, 0, 0, 0) 0px 0px 0px 0px, rgba(0, 0, 0, 0) 0px 0px 0px 0px, rgba(0, 0, 0, 0) 0px 0px 0px 0px, rgba(0, 0, 0, 0) 0px 0px 0px 0px, rgba(0, 0, 0, 0.05) 0px 0px 3px 0px, rgba(0, 0, 0, 0.05) 0px 8px 12px 0px, rgba(0, 0, 0, 0.05) 0px 12px 20px 0px;
  --ease-1: cubic-bezier(0, 0, 0.6, 1);
  --ease-2: cubic-bezier(0, 0, 0.2, 1);
  --ease-3: cubic-bezier(0.4, 0, 0.2, 1);
  --ease-4: cubic-bezier(0.76, 0, 0.24, 1);
}
```
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)", "text-muted": "var(--color-text-muted)", "action": "var(--color-action)", "on-action": "var(--color-on-action)" },
  fontFamily: { "body": ["var(--font-body)"], "display": ["var(--font-display)"] },
  borderRadius: { "sm": "var(--radius-sm)", "md": "var(--radius-md)", "lg": "var(--radius-lg)", "3xl": "var(--radius-3xl)", "full": "var(--radius-full)" },
  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); color: var(--color-text); -webkit-font-smoothing: antialiased; -moz-osx-font-smoothing: grayscale; }
h1, h2, h3 { font-family: var(--font-display); margin: 0; }
a { color: inherit; }
:focus-visible { outline: 2px solid var(--color-action); outline-offset: 2px; }
```

3. COMPONENTS — MATCH THESE EXACTLY
```css
.card { /* Default */
  border: 1px solid #AFB2CE;
  border-radius: var(--radius-3xl);
  padding: 0px 3px 0px 0px;
  min-height: 48px;
  color: #000000;
  font-family: var(--font-body);
  font-size: var(--type-body);
  font-weight: 400;
  line-height: 24px;
  /* recorded states: hover */
}
.button { /* Primary */
  background: var(--color-action);
  border: 1px solid #AFB2CE;
  border-radius: var(--radius-full);
  min-height: 40px;
  color: var(--color-on-action);
  font-family: var(--font-body);
  font-size: var(--type-body);
  font-weight: 420;
  line-height: 16px;
  /* recorded states: hover, focus-visible, active */
}
.button-2 { /* Secondary */
  background: var(--color-action);
  border-radius: var(--radius-full);
  min-height: 40px;
  color: var(--color-text);
  font-family: var(--font-body);
  font-size: var(--type-body);
  font-weight: 420;
  line-height: 16px;
  /* recorded states: hover, focus-visible, active */
}
.button-3 { /* Secondary 2 */
  border-radius: var(--radius-3xl);
  padding: 0px 20px 0px 20px;
  min-height: 40px;
  color: var(--color-ffffff);
  font-family: var(--font-body);
  font-size: var(--type-body);
  font-weight: 420;
  line-height: 16px;
  /* recorded states: hover, focus-visible, active */
}
.link { /* Inline */
  background: transparent;
  border-radius: var(--radius-sm);
  color: var(--color-text);
  font-family: var(--font-body);
  font-size: var(--type-body);
  font-weight: 400;
  line-height: 22.4px;
  /* recorded states: hover, focus-visible, active */
}
.link-2 { /* Inline 2 */
  background: transparent;
  border-radius: var(--radius-sm);
  color: var(--color-text);
  font-family: var(--font-body);
  font-size: var(--type-body);
  font-weight: 480;
  line-height: 21.6px;
  /* recorded states: hover, focus-visible, active */
}
.link-3 { /* Inline 3 */
  background: transparent;
  border-radius: var(--radius-40);
  padding: 0px 20px 0px 20px;
  min-height: 40px;
  color: var(--color-text);
  font-family: var(--font-body);
  font-size: var(--type-body);
  font-weight: 420;
  line-height: 16px;
  /* recorded states: focus-visible, active, hover */
}
.input { /* Default */
  background: transparent;
  border-radius: 32px 0px 0px 32px;
  padding: 0px 0px 0px 20px;
  min-height: 46px;
  color: var(--color-text);
  font-family: var(--font-body);
  font-size: var(--type-body);
  font-weight: 420;
  line-height: 16px;
}
```
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
- Dark interface on #171721. Keep that ground; do not add a light mode.
- The opening screen carries a large image or video behind or across the heading. 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 #FCFCFA and Background (#171721); use only those.
- #9CB4E8 is the action colour. Fill the primary action with it and little else — at most one #9CB4E8-filled element per screen; other accents keep to the uses listed above.
- Type: Figtree (standing in for arcadia) for body; Archivo (standing in for arcadiaDisplay) for display. Hierarchy comes from size and weight, not colour or decoration.
- Everything sits on a 8px grid.
- Corner radii are 4px, 8px, 12px, 32px, fully round (pill) — nothing else.
- Body text uses arcadia at around 16px, weights 360, 400, 420, 480, 700.
- Headings use arcadiaDisplay; the largest heading is 65.34px.
- Primary buttons are #9CB4E8, pill-shaped, weight 420.
- Cards use 32px corners.
- Spacing follows a 4px rhythm (1, 2, 3, 4, 8, 12, 16).
- Corner radii in use: 4px, 12px, 8px, 40px, 9999px (pill).

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 — 900px tall, centred 49.35px heading (weight 480), image behind the content, on #171721.
2. Text — 972px tall, left-aligned 24px heading (weight 480), image behind the content, on #171721.
3. Statement — 393px tall, centred 42px heading (weight 480).
4. Cards — 668px tall, 3 equal columns, 4px gap, left-aligned 21.01px heading (weight 480) set low in the band, image centred.
5. Grid — 1130px tall, 4 items in 2 columns with 32px gaps, left-aligned 32px heading (weight 480), image on the left.
6. Statement — 338px tall, centred 28px heading (weight 360).
7. Split — 732px tall, 2 equal columns, 32px gap, left-aligned 24px heading (weight 480), image on the right.
8. Split — 712px tall, 2 equal columns, 32px gap, left-aligned 24px heading (weight 480), image on the left.
9. Grid — 1045px tall, 4 items in 2 columns with 32px gaps, left-aligned 32px heading (weight 480), image on the left.
10. Cards — 449px tall, 4 equal columns, centred 65.34px heading (weight 480) set low in the band.
11. Cards — 744px tall, 3 equal columns, 32px gap, left-aligned 32px heading (weight 480), image on the left.
12. Cards — 621px tall, 3 equal columns, 32px gap, left-aligned 32px heading (weight 480), image on the left.
13. Split — 787px tall, 2 equal columns, 32px gap, centred 42px heading (weight 480).
14. Grid — 909px tall, 8 items in 4 columns with 40px gaps, left-aligned 16px heading (weight 400), on #171721.
15. Footer — 1211px tall, split 4 / 8, left-aligned 12px heading (weight 400), on #171721.
- Content runs 1024px wide with 208px side margins at 1440px; there is no narrower centred container.
- A 72px header scrolls away.
- The hero is 900px (exactly one screen): centred 49.35px heading (weight 480), image behind the content, on #171721.
- Column splits on a 12-column grid: halves (5×), thirds (3×), quarters (2×), 4/8; gaps of 32px.
- Headings align left (10 of 15 sections); centre only the occasional statement.
- Sections share one background; they are separated by space and lines, not colour bands.
- A typical section is about 732px tall.

COPY SHAPE (MATCH THE LENGTH AND CASE; WRITE YOUR OWN WORDS)
- The main heading is 3 words long.
- Section headings are medium length: typically 5 words.
- Headings are in sentence case (only the first word capitalised).
- The page describes itself in about 21 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 1024px wide, centred, with var(--space-4) (16px) side padding on small screens.
- The largest heading scales fluidly: font-size: clamp(32px, 4.5vw, 65.34px). 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 (15.2:1), Text muted on Background (10.2:1), Action on Background (8.6:1), Text on Surface (12.6:1), Text muted on Surface (8.4:1), Action on Surface (7.1:1) and On action on Action (10.1:1).
- 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: #171721, #FFFFFF, #EDEDF3, #1E1E2A, #C3C3CC, #FCFCFA, #70707D, #2A2924, #272735, #9CB4E8, #000000. 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.)
- #5266EB only as small fills (buttons, badges) — never a section background or a large panel. (It covers under 0.1% of the page.)
- #CDDDFF only as small fills (buttons, badges) — never a section background or a large panel. (It covers under 0.1% of the page.)
- Only the fonts in the tokens: Figtree for body; Archivo for display. No other typeface, and no Inter, Roboto or system UI font unless it is one of these. (The page is set in arcadia and arcadiaDisplay; the tokens carry what stands in for them.)
- Headings and large text never heavier than weight 480. Do not make headlines bold to add emphasis. (Every size from 24px up is set at weight 480 or lighter.)
- No all-caps eyebrow labels above headings. (No uppercase text was measured.)
- 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, text, statement, cards, grid, split, 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 mercury.com'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.
- #5266EB covers about 0.1% of the page or less, as on the original.
- #CDDDFF covers about 0.1% of the page or less, as on the original.
- No text 24px or larger has a font-weight above 480.
- Every section, including ones the original does not have, uses only this system's colours, type, shapes and spacing.
- 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.