What is a Design System?

A design system is a collection of reusable components, guided by clear standards, that can be assembled to build any number of applications.

Design Tokens

:root {
  /* Colors */
  --color-primary-50: #eff6ff;
  --color-primary-500: #3b82f6;
  --color-primary-900: #1e3a8a;
  
  --color-gray-50: #f9fafb;
  --color-gray-500: #6b7280;
  --color-gray-900: #111827;
  
  /* Semantic colors */
  --color-success: #10b981;
  --color-warning: #f59e0b;
  --color-error: #ef4444;
  
  /* Typography */
  --font-sans: 'Inter', system-ui, sans-serif;
  --font-mono: 'Fira Code', monospace;
  
  --text-xs: 0.75rem;
  --text-sm: 0.875rem;
  --text-base: 1rem;
  --text-lg: 1.125rem;
  --text-xl: 1.25rem;
  --text-2xl: 1.5rem;
  
  /* Spacing */
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-4: 1rem;
  --space-8: 2rem;
  --space-16: 4rem;
  
  /* Shadows */
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1);
  
  /* Border radius */
  --radius-sm: 0.25rem;
  --radius-md: 0.375rem;
  --radius-lg: 0.5rem;
  --radius-full: 9999px;
}

Dark Mode with Custom Properties

:root {
  --bg-primary: var(--color-gray-50);
  --bg-secondary: white;
  --text-primary: var(--color-gray-900);
  --text-secondary: var(--color-gray-500);
  --border-color: var(--color-gray-200);
}

[data-theme='dark'] {
  --bg-primary: var(--color-gray-900);
  --bg-secondary: var(--color-gray-800);
  --text-primary: var(--color-gray-50);
  --text-secondary: var(--color-gray-400);
  --border-color: var(--color-gray-700);
}

/* Usage */
.card {
  background: var(--bg-secondary);
  color: var(--text-primary);
  border: 1px solid var(--border-color);
}

Component Variants

/* Button component with variants */
.button {
  /* Base styles */
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-weight: 500;
  border-radius: var(--radius-md);
  transition: all 0.15s ease;
  
  /* Size variants */
  &.button--sm {
    padding: var(--space-1) var(--space-2);
    font-size: var(--text-sm);
  }
  
  &.button--md {
    padding: var(--space-2) var(--space-4);
    font-size: var(--text-base);
  }
  
  &.button--lg {
    padding: var(--space-4) var(--space-8);
    font-size: var(--text-lg);
  }
  
  /* Color variants */
  &.button--primary {
    background: var(--color-primary-500);
    color: white;
    
    &:hover {
      background: var(--color-primary-600);
    }
  }
  
  &.button--secondary {
    background: var(--bg-secondary);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
    
    &:hover {
      background: var(--color-gray-100);
    }
  }
  
  &.button--ghost {
    background: transparent;
    color: var(--color-primary-500);
    
    &:hover {
      background: var(--color-primary-50);
    }
  }
}

Container Queries

/* Card that adapts to its container */
.card-container {
  container-type: inline-size;
  container-name: card;
}

.card {
  display: grid;
  gap: var(--space-4);
  padding: var(--space-4);
}

/* Switch to horizontal layout in larger containers */
@container card (min-width: 400px) {
  .card {
    grid-template-columns: 150px 1fr;
  }
  
  .card__image {
    aspect-ratio: 1;
  }
}

@container card (min-width: 600px) {
  .card {
    grid-template-columns: 200px 1fr;
    padding: var(--space-8);
  }
}

Modern Layout Patterns

/* Auto-fit grid */
.grid-auto {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 300px), 1fr));
  gap: var(--space-4);
}

/* Holy grail layout with subgrid */
.layout {
  display: grid;
  grid-template-rows: auto 1fr auto;
  min-height: 100vh;
}

/* Stack pattern */
.stack {
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
}

/* Cluster pattern */
.cluster {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
}

/* Center pattern */
.center {
  display: grid;
  place-items: center;
}

Animation Tokens

:root {
  --duration-fast: 150ms;
  --duration-normal: 300ms;
  --duration-slow: 500ms;
  
  --ease-in: cubic-bezier(0.4, 0, 1, 1);
  --ease-out: cubic-bezier(0, 0, 0.2, 1);
  --ease-in-out: cubic-bezier(0.4, 0, 0.2, 1);
  --ease-spring: cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

.fade-in {
  animation: fadeIn var(--duration-normal) var(--ease-out);
}

@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

.slide-up {
  animation: slideUp var(--duration-normal) var(--ease-spring);
}

@keyframes slideUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
}

Conclusion

A good design system provides consistency, speeds up development, and makes maintenance easier. Start with tokens, build components, and document everything.