Skip to main content

Project 3: Modular Design System Component Library

In this hands-on project, you will build a scalable, production-grade Design System Component Library.

You will structure reusable CSS design primitives—including action controls, data display components, form controls, and feedback indicators—using Design Tokens, dynamic theme switching via :has(), and standard BEM syntax.

Technical Specifications & Requirements​

Review the core architectural and structural specifications for building this component library:

  1. Token-Driven Architecture:

    • Global design tokens defined via :root CSS custom properties for spacing scale, color palettes, typography, and elevation shadows.
    • Scoped component tokens for fine-grained component override flexibility.

  2. Component Primitives Suite:

    • Buttons: Multi-variant support (primary, secondary, ghost, danger) and state triggers (:hover, :active, :focus-visible).
    • Cards: Flexible structure featuring header, content body, and action footer zones.
    • Forms: Custom styled inputs, labels, and validation focus state treatments.
    • Badges & Tags: Semantic color indicators (success, warning, info, danger).

  3. Modern CSS Features & Accessibility:

    • Modern state-driven theme switching using :has() selectors.
    • Clear :focus-visible outline rings for keyboard navigation compliance.

Interactive Project Implementation​

Inspect and test the modular component library system below:

Loading Interactive Editor...

Technical Architectural Insights​

1. Zero-JS Dark Mode via :has()​

Instead of adding JavaScript to toggle class names, we leverage the native CSS parent selector :has():

:has(#theme-switch:checked) {
  --ch-color-bg: #0f172a;
  --ch-color-surface: #1e293b;
  --ch-color-border: #334155;
  --ch-color-text-main: #f8fafc;
}

When the user checks #theme-switch, :has() detects the change and dynamically updates the root CSS tokens.

2. Accessible Focus Management​

Accessibility is built directly into every interactive component primitive using :focus-visible:

.ch-btn:focus-visible {
  outline: none;
  box-shadow: var(--ch-focus-ring);
}

  • :focus-visible: Prevents unsightly blue focus outlines for mouse clicks while ensuring high-contrast focus rings display for keyboard users pressing Tab.

Key Takeaways​

  • Design tokens store baseline design values in custom properties, enabling effortless global updates.
  • BEM naming conventions (.block__element--modifier) keep class names clear and prevent cascading selector conflicts.
  • Combining accessibility triggers like :focus-visible with state selectors like :has() produces accessible, interactive UI components using pure CSS.