Substack — Design System

light · modern · medium · custom · confidence 92%

The full decoded design system for Substack: color roles, type scale, spacing, radii and paste-ready DESIGN.md / Tailwind / CSS exports.

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This is a static, crawlable rendering for search & AI engines. The interactive version — filters, live decode console, copy & export — is at https://mozaika.design/ds/substack.

Tokens

Substack's decoded design system: background #FFFFFF, text #363737, accent #0083D5, link #0083D5, primary #FF6719; type scale h1 19px / h2 19px / body 15px; 8px spacing base; 8px base radius. The single interactive/action color is #FFFFFF — used only on interactive or must-notice elements (buttons, links, key highlights), never on large fills.

Color roles

Using these colors

• Action color #FFFFFF — the single interactive color; only on things you click or must notice, never large fills.
• accent, link are all #0083D5 — one role, not several (the action color).
• accent #0083D5 — accent for emphasis — keep it rare on the page.
• primary #FF6719 — a brand color — but the call-to-action uses #FFFFFF, not this.

Typography

• Heading: Segoe UI
• Body: Segoe UI
• h1: 19px
• h2: 19px
• body: 15px

Spacing

• base unit: 8px
• scale: 4px, 8px, 12px, 16px, 24px, 32px, 48px, 64px

Radii

• base: 8px
• button: 8px

Shadow

rgba(0, 0, 0, 0.1) 0px 4px 6px -1px, rgba(0, 0, 0, 0.06) 0px 2px 4px -1px

Export: DESIGN.md

# Substack — Design System

> light, modern, medium, custom

## Colors

| Role | Value |
|------|-------|
| bg | `#FFFFFF` |
| surface | `#F2F3F3` |
| border | `#E0E1E1` |
| text | `#363737` |
| text_muted | `#828383` |
| primary | `#FF6719` |
| accent | `#0083D5` |
| link | `#0083D5` |
| button_bg | `#FFFFFF` |
| button_text | `#363737` |

**Using these colors**

- **Action color** `#FFFFFF` — the single interactive color; it appears only on things you click or must notice (buttons, key highlights), never on large fills or backgrounds.
- `accent`, `link` are all `#0083D5` — one role, not several.
- **accent** `#0083D5` — accent for emphasis — keep it rare on the page.
- **primary** `#FF6719` — a brand color — but the call-to-action uses #FFFFFF, not this.

## Typography

- Heading: **Segoe UI** _(free fallback: Newsreader)_
- Body: **Segoe UI** _(free fallback: Newsreader)_
- h1: 19px
- h2: 19px
- body: 15px

> **Fonts —** Segoe UI may be proprietary — safe free fallback: Newsreader (Google Fonts).

## Spacing
- base unit: 8px
- scale: 4px, 8px, 12px, 16px, 24px, 32px, 48px, 64px

## Radius
- base: 8px
- button: 8px

## Primary button
- bg `#FFFFFF` · text `#363737` · radius 8px

## How to apply
Paste the Tailwind `@theme` (or CSS variables) as your base, then build each
section to its spec — verify every color, radius, and font against these tokens.

Export: Tailwind v4 (@theme)

@theme {
  /* action color #FFFFFF — the one interactive color; buttons/links/emphasis only, never large fills. */
  --color-bg: #FFFFFF;
  --color-surface: #F2F3F3;
  --color-border: #E0E1E1;
  --color-text: #363737;
  --color-text-muted: #828383;
  --color-primary: #FF6719;  /* a brand color — but the call-to-action uses #FFFFFF, not this. */
  --color-accent: #0083D5;  /* accent for emphasis — keep it rare on the page. */
  --color-link: #0083D5;  /* inline text links and link-styled controls. */
  --color-button-bg: #FFFFFF;  /* primary-button fill — the main call-to-action color. */
  --color-button-text: #363737;
  /* fonts: Segoe UI may be proprietary — safe free fallback: Newsreader (Google Fonts). */
  --font-heading: "Segoe UI", "Newsreader", system-ui, -apple-system, 'Segoe UI', sans-serif;
  --font-body: "Segoe UI", "Newsreader", system-ui, -apple-system, 'Segoe UI', sans-serif;
  --text-h1: 19px;
  --text-h2: 19px;
  --text-body: 15px;
  --radius-base: 8px;
  --radius-button: 8px;
  --spacing-1: 4px;
  --spacing-2: 8px;
  --spacing-3: 12px;
  --spacing-4: 16px;
  --spacing-5: 24px;
  --spacing-6: 32px;
  --spacing-7: 48px;
  --spacing-8: 64px;
}

Export: CSS variables

:root {
  /* action color #FFFFFF — the one interactive color; buttons/links/emphasis only, never large fills. */
  --bg: #FFFFFF;
  --surface: #F2F3F3;
  --border: #E0E1E1;
  --text: #363737;
  --text-muted: #828383;
  --primary: #FF6719;  /* a brand color — but the call-to-action uses #FFFFFF, not this. */
  --accent: #0083D5;  /* accent for emphasis — keep it rare on the page. */
  --link: #0083D5;  /* inline text links and link-styled controls. */
  --button-bg: #FFFFFF;  /* primary-button fill — the main call-to-action color. */
  --button-text: #363737;
  --font-heading: "Segoe UI", "Newsreader", system-ui, -apple-system, 'Segoe UI', sans-serif;
  --font-body: "Segoe UI", "Newsreader", system-ui, -apple-system, 'Segoe UI', sans-serif;
  --radius: 8px;
  --radius-button: 8px;
}
/* fonts: Segoe UI may be proprietary — safe free fallback: Newsreader (Google Fonts). */