.header {
  position: sticky;
  top: 0;
  z-index: 20;
  display: flex;
  align-items: center;
  min-height: var(--header-height);
  border-bottom: var(--border-width) solid var(--color-line);
  background: var(--color-header-bg);
  -webkit-backdrop-filter: blur(var(--blur-glass));
  backdrop-filter: blur(var(--blur-glass));
}

.header__inner {
  display: flex;
  align-items: center;
  gap: var(--space-xs);
}

.header__brand {
  display: inline-flex;
  align-items: center;
  gap: var(--space-xs);
  font-size: var(--text-s);
  font-weight: var(--font-weight-bold);
  letter-spacing: -0.02em;
  margin-right: auto;
}

.header__brand-mark {
  display: grid;
  place-items: center;
  width: 2rem;
  height: 2rem;
  border: var(--border-width) solid var(--color-line-strong);
  border-radius: var(--radius-s);
  background: var(--gradient-brand-mark);
  color: var(--color-accent);
  font-size: var(--text-xs);
}

/* Icon buttons: theme switch and mobile burger */
.header__theme,
.header__toggle {
  display: inline-grid;
  place-content: center;
  gap: var(--space-3xs);
  width: 2.75rem; /* 44 — primary mobile control */
  height: 2.75rem;
  border: var(--border-width) solid var(--color-line);
  border-radius: var(--radius-s);
  color: var(--color-text);
}

/* Icon shows the theme a click switches to: sun in dark, moon in light */
.header__theme-icon--moon {
  display: none;
}

@media (prefers-color-scheme: light) {
  :root:not([data-theme="dark"]) .header__theme-icon--sun {
    display: none;
  }

  :root:not([data-theme="dark"]) .header__theme-icon--moon {
    display: block;
  }
}

:root[data-theme="light"] .header__theme-icon--sun {
  display: none;
}

:root[data-theme="light"] .header__theme-icon--moon {
  display: block;
}

.header__toggle-line {
  display: block;
  width: 1.125rem;
  height: 2px;
  border-radius: 1px;
  background: currentColor;
}

/* Lines fold into a cross: offset = line height + gap */
.header__toggle[aria-expanded="true"] .header__toggle-line:nth-child(1) {
  transform: translateY(6px) rotate(45deg);
}

.header__toggle[aria-expanded="true"] .header__toggle-line:nth-child(2) {
  opacity: 0;
}

.header__toggle[aria-expanded="true"] .header__toggle-line:nth-child(3) {
  transform: translateY(-6px) rotate(-45deg);
}

/* Mobile: dropdown panel under the header, opened by js/modules/menu.js */
.header__nav {
  display: none;
  position: absolute;
  top: 100%;
  left: 0;
  right: 0;
  padding: var(--space-2xs) var(--container-gutter) var(--space-m);
  border-bottom: var(--border-width) solid var(--color-line);
  background: var(--color-bg);
}

.header__nav.is-open {
  display: block;
}

.header__menu {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  list-style: none;
}

.header__link {
  display: inline-flex;
  align-items: center;
  gap: var(--space-3xs);
  min-height: 2.75rem; /* 44 — mobile touch target */
  color: var(--color-text-muted);
  font-size: var(--text-s);
}

.header__link--github {
  padding-inline: var(--space-xs);
  border: var(--border-width) solid var(--color-line);
  border-radius: var(--radius-s);
  color: var(--color-text);
}

@media (min-width: 768px) {
  .header__inner {
    gap: var(--space-m);
  }

  .header__toggle {
    display: none;
  }

  /* After the menu on desktop; before the burger in DOM so mobile focus order stays logical */
  .header__theme {
    order: 1;
    width: 2.25rem;
    height: 2.25rem;
  }

  .header__nav {
    display: block;
    position: static;
    padding: 0;
    border-bottom: none;
    background: none;
  }

  .header__menu {
    flex-direction: row;
    align-items: center;
    gap: var(--space-m);
  }

  .header__link {
    min-height: 2.25rem; /* 36 — touch target ≥ 24px */
  }
}

@media (hover: hover) {
  .header__link:hover {
    color: var(--color-text);
  }

  .header__theme:hover,
  .header__toggle:hover {
    border-color: var(--color-line-hover);
  }
}

@media (prefers-reduced-motion: no-preference) {
  .header__toggle-line {
    transition: transform var(--duration-fast) var(--ease-standard), opacity var(--duration-fast) var(--ease-standard);
  }
}