design-tokens-theming

Design Tokens & Theming

Overview

A SaaS UI looks "designed" when every color, space, and font size comes from a small, named scale — not arbitrary values sprinkled per component. Define tokens once as CSS variables, expose them through Tailwind, and let dark mode be a swap of variable values, not a rewrite of class names.

When to use

• Starting a new app and deciding colors/spacing/typography.
• Components use raw hex codes or one-off pixel values.
• You need dark mode or multi-brand theming.

Semantic tokens (the key idea)

Name tokens by role, not by hue. --primary, --muted, --destructive — not --blue-500. Roles let you re-theme without touching components. shadcn/ui uses exactly this convention:

/* globals.css */
:root {
  --background: 0 0% 100%;
  --foreground: 240 10% 3.9%;
  --primary: 240 5.9% 10%;
  --primary-foreground: 0 0% 98%;
  --muted: 240 4.8% 95.9%;
  --muted-foreground: 240 3.8% 46.1%;
  --destructive: 0 84.2% 60.2%;
  --border: 240 5.9% 90%;
  --radius: 0.5rem;
}
.dark {
  --background: 240 10% 3.9%;
  --foreground: 0 0% 98%;
  --primary: 0 0% 98%;
  --primary-foreground: 240 5.9% 10%;
  --muted: 240 3.7% 15.9%;
  --muted-foreground: 240 5% 64.9%;
  --border: 240 3.7% 15.9%;
}

Store HSL channels (no hsl(...) wrapper) so Tailwind can add opacity: hsl(var(--primary) / 0.5).

Wire tokens into Tailwind

// tailwind.config.ts
export default {
  darkMode: "class",
  theme: {
    extend: {
      colors: {
        background: "hsl(var(--background))",
        foreground: "hsl(var(--foreground))",
        primary: { DEFAULT: "hsl(var(--primary))", foreground: "hsl(var(--primary-foreground))" },
        muted: { DEFAULT: "hsl(var(--muted))", foreground: "hsl(var(--muted-foreground))" },
        border: "hsl(var(--border))",
      },
      borderRadius: { lg: "var(--radius)", md: "calc(var(--radius) - 2px)" },
    },
  },
};

Now bg-primary text-primary-foreground works in both themes automatically.

Dark mode toggle

Use next-themes (or a tiny class toggler) and darkMode: "class". Never hard-code dark: colors when a semantic token already flips — bg-background beats bg-white dark:bg-zinc-950.

Scales to standardize

• Spacing: stick to Tailwind's 4px scale (p-2, gap-4, space-y-6). Avoid p-[13px].
• Typography: a 5–6 step type scale (text-sm→text-3xl); set text-muted-foreground for secondary text.
• Radius/shadow: one --radius token; 2–3 shadow steps.

Pitfalls

• Raw hex/px values per component → inconsistent UI that can't be re-themed.
• `dark:` overrides everywhere instead of flipping tokens once.
• Naming tokens by color (--blue) instead of role (--primary).
• Wrapping `hsl()` in the variable — breaks Tailwind opacity modifiers.
• Too many shades — a bloated palette is harder to keep consistent than a tight one.

Hand-off

A token layer that responsive-layout, accessible-components, and every component skill build on — change a value once, the whole app re-themes.