/* =============================================================================
   NEXUS — Shell
   The persistent frame: masthead, brand signature, appearance control,
   content region and footer baseline.
   ========================================================================== */

@layer components {
  /* ---------------------------------------------------------------------
     Masthead
     ------------------------------------------------------------------ */
  .site-header {
    position: sticky;
    inset-block-start: 0;
    z-index: var(--z-header);
    background-color: color-mix(in oklab, var(--color-canvas) 78%, transparent);
    backdrop-filter: saturate(180%) blur(16px);
    -webkit-backdrop-filter: saturate(180%) blur(16px);
    border-block-end: 1px solid transparent;
    transition: border-color var(--duration-base) var(--ease-standard),
      background-color var(--duration-base) var(--ease-standard);
  }

  /* Set once the page has left the top; keeps the header weightless at rest. */
  .site-header[data-scrolled="true"] {
    background-color: color-mix(in oklab, var(--color-canvas) 88%, transparent);
    border-block-end-color: var(--color-border);
  }

  .site-header__inner {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: var(--space-6);
    block-size: var(--header-height);
  }

  /* ---------------------------------------------------------------------
     Brand signature
     ------------------------------------------------------------------ */
  .brand {
    display: inline-flex;
    align-items: center;
    gap: var(--space-3);
    color: var(--color-text);
    text-decoration: none;
    border-radius: var(--radius-sm);
  }

  .brand__mark {
    inline-size: 1.75rem;
    block-size: 1.75rem;
    color: var(--color-accent);
    transition: color var(--duration-base) var(--ease-standard);
  }

  .brand:hover .brand__mark {
    color: var(--color-accent-hover);
  }

  .brand__word {
    font-size: var(--text-md);
    font-weight: var(--weight-semibold);
    letter-spacing: var(--tracking-tight);
  }

  /* ---------------------------------------------------------------------
     Appearance control
     ------------------------------------------------------------------ */
  .theme-toggle {
    display: inline-grid;
    place-items: center;
    inline-size: 2.25rem;
    block-size: 2.25rem;
    border-radius: var(--radius-full);
    color: var(--color-text-muted);
    box-shadow: var(--shadow-ring);
    transition: color var(--duration-fast) var(--ease-standard),
      background-color var(--duration-fast) var(--ease-standard);
  }

  .theme-toggle:hover {
    background-color: var(--color-surface-raised);
    color: var(--color-text);
  }

  .theme-toggle__icon {
    grid-area: 1 / 1;
    inline-size: 1.125rem;
    block-size: 1.125rem;
    transition: opacity var(--duration-base) var(--ease-out),
      transform var(--duration-base) var(--ease-spring);
  }

  /* Dark is the base: the sun is offered, the moon is held back. */
  .theme-toggle__icon[data-icon="moon"] {
    opacity: 0;
    transform: rotate(-45deg) scale(0.6);
  }

  :root[data-theme="light"] .theme-toggle__icon[data-icon="sun"] {
    opacity: 0;
    transform: rotate(45deg) scale(0.6);
  }

  :root[data-theme="light"] .theme-toggle__icon[data-icon="moon"] {
    opacity: 1;
    transform: none;
  }

  /* ---------------------------------------------------------------------
     Content region
     ------------------------------------------------------------------ */
  .site-main {
    display: block;
  }

  /* ---------------------------------------------------------------------
     Footer baseline
     ------------------------------------------------------------------ */
  .site-footer {
    border-block-start: 1px solid var(--color-border);
    background-color: var(--color-surface-sunken);
  }

  .site-footer__inner {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    justify-content: space-between;
    gap: var(--space-4);
    padding-block: var(--space-8);
    color: var(--color-text-subtle);
    font-size: var(--text-sm);
  }
}