Behavior reference

Behaviors read attributes. Your JavaScript, in any framework, sets them; the stylesheet and assistive technology read the same markup.

States

• data-state="loading"
• data-state="success"
• data-state="error"
• data-state="warning"
• data-state="info"
• data-state="active"
• data-state="disabled"
• data-state="idle"
• data-state="hidden"

Motion

• data-motion="fade"
• data-motion="slide-up"
• data-motion="scale"
• data-motion="interactive"

Every [data-motion] element drops its transitions and animations under prefers-reduced-motion: reduce.

ARIA attributes with styles

• [aria-disabled="true"]
• [aria-live]

Source

states.css

@layer behaviors {
  /* Loading state */
  [data-state="loading"] {
    position: relative;
    color: transparent;
    pointer-events: none;
  }

  [data-state="loading"]::after {
    content: '';
    position: absolute;
    inset: 0;
    margin: auto;
    inline-size: 1.25em;
    block-size: 1.25em;
    border-radius: 50%;
    border: 2px solid currentColor;
    border-inline-end-color: transparent;
    animation: spin var(--motion-duration-slower) linear infinite;
    color: var(--color-text-on-interactive);
  }

  @keyframes spin {
    to {
      rotate: 1turn;
    }
  }

  /* Success state */
  [data-state="success"] {
    background: var(--color-status-success-bg);
    color: var(--color-status-success-text);
    border-color: var(--color-status-success-border);
  }

  /* Error state */
  [data-state="error"] {
    background: var(--color-status-error-bg);
    color: var(--color-status-error-text);
    border-color: var(--color-status-error-border);
  }

  /* Warning state */
  [data-state="warning"] {
    background: var(--color-status-warning-bg);
    color: var(--color-status-warning-text);
    border-color: var(--color-status-warning-border);
  }

  /* Info state */
  [data-state="info"] {
    background: var(--color-status-info-bg);
    color: var(--color-status-info-text);
    border-color: var(--color-status-info-border);
  }

  /* Active state */
  [data-state="active"] {
    background: var(--color-bg-interactive);
    color: var(--color-text-on-interactive);
    border-color: var(--color-border-interactive);
  }

  /* Disabled state */
  [data-state="disabled"],
  [disabled] {
    opacity: 0.5;
    pointer-events: none;
    cursor: not-allowed;
  }

  /* Interactive states for buttons specifically */
  button[data-state="idle"]:hover {
    background: var(--color-bg-interactive-hover);
  }

  button[data-state="idle"]:active {
    background: var(--color-bg-interactive-active);
    transform: scale(0.98);
  }
}

motion.css

@layer behaviors {
  /* Fade motion */
  [data-motion="fade"] {
    transition: opacity var(--motion-duration-base) var(--motion-easing-out);
  }

  [data-motion="fade"][data-state="hidden"],
  [data-motion="fade"][hidden] {
    opacity: 0;
  }

  /* Slide up motion */
  [data-motion="slide-up"] {
    transition:
      transform var(--motion-duration-base) var(--motion-easing-out),
      opacity var(--motion-duration-base) var(--motion-easing-out);
  }

  [data-motion="slide-up"][data-state="hidden"],
  [data-motion="slide-up"][hidden] {
    transform: translateY(1rem);
    opacity: 0;
  }

  /* Scale motion */
  [data-motion="scale"] {
    transition:
      transform var(--motion-duration-base) var(--motion-easing-spring),
      opacity var(--motion-duration-base) var(--motion-easing-out);
  }

  [data-motion="scale"][data-state="hidden"],
  [data-motion="scale"][hidden] {
    transform: scale(0.95);
    opacity: 0;
  }

  /* Interactive motion hints */
  [data-motion="interactive"] {
    transition: transform var(--motion-duration-fast) var(--motion-easing-out);
  }

  /* Only where the pointer can hover: on a touch screen a tap would leave
     the element lifted. */
  @media (hover: hover) {
    [data-motion="interactive"]:hover {
      transform: translateY(-2px);
    }
  }

  [data-motion="interactive"]:active {
    transform: translateY(0);
  }

  /* Reduced motion support */
  @media (prefers-reduced-motion: reduce) {
    [data-motion],
    [data-motion] * {
      animation-duration: 0.01ms !important;
      animation-iteration-count: 1 !important;
      transition-duration: 0.01ms !important;
      scroll-behavior: auto !important;
    }
  }

  /* Duration utilities */
  [data-motion-duration="fast"] {
    --motion-duration: var(--motion-duration-fast);
  }

  [data-motion-duration="base"] {
    --motion-duration: var(--motion-duration-base);
  }

  [data-motion-duration="slow"] {
    --motion-duration: var(--motion-duration-slow);
  }

  /* Easing utilities */
  [data-motion-easing="linear"] {
    --motion-easing: var(--motion-easing-linear);
  }

  [data-motion-easing="in"] {
    --motion-easing: var(--motion-easing-in);
  }

  [data-motion-easing="out"] {
    --motion-easing: var(--motion-easing-out);
  }

  [data-motion-easing="in-out"] {
    --motion-easing: var(--motion-easing-inOut);
  }

  [data-motion-easing="spring"] {
    --motion-easing: var(--motion-easing-spring);
  }
}

accessibility.css

@layer behaviors {
  /* Screen reader only */
  .sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border-width: 0;
  }

  /* Focus visible styles */
  :focus-visible {
    outline: 2px solid var(--color-border-focus);
    outline-offset: 2px;
    border-radius: var(--radius-sm);
  }

  /* Skip link */
  .skip-link {
    position: absolute;
    top: var(--space-2);
    left: var(--space-2);
    padding: var(--space-2) var(--space-4);
    background: var(--color-bg-interactive);
    color: var(--color-text-on-interactive);
    border-radius: var(--radius-md);
    text-decoration: none;
    transform: translateY(-200%);
    transition: transform var(--motion-duration-fast) var(--motion-easing-out);
    z-index: 9999;
  }

  .skip-link:focus {
    transform: translateY(0);
  }

  /* Focus within - show focus indicator for parent when child is focused */
  [data-focus-within]:focus-within {
    outline: 2px solid var(--color-border-focus);
    outline-offset: 2px;
  }

  /* Keyboard navigation indicator */
  :focus:not(:focus-visible) {
    outline: none;
  }

  /* Disabled interactive elements */
  [aria-disabled="true"] {
    opacity: 0.5;
    cursor: not-allowed;
    pointer-events: none;
  }

  /* Live regions for announcements */
  [aria-live] {
    position: absolute;
    left: -10000px;
    width: 1px;
    height: 1px;
    overflow: hidden;
  }

  [aria-live][data-visible] {
    position: static;
    width: auto;
    height: auto;
  }

  /* High contrast mode support */
  @media (prefers-contrast: high) {
    :focus-visible {
      outline-width: 3px;
      outline-offset: 3px;
    }

    button,
    input,
    select,
    textarea {
      border-width: 2px;
    }
  }

  /* Respect prefers-reduced-transparency */
  @media (prefers-reduced-transparency: reduce) {
    * {
      backdrop-filter: none !important;
    }
  }
}