/* --- sticky topbar: logo · search (middle) · nav (right) --- */
.site-header {
  border-bottom: 1px solid var(--color-rule);
  background: var(--color-bg);
  position: sticky;
  top: 0;
  z-index: 10;
  backdrop-filter: saturate(180%) blur(8px);
}
.site-header__inner {
  max-width: var(--max-w);
  margin-inline: auto;
  padding: 1rem 1.25rem;
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto minmax(0, 1fr);
  align-items: center;
  gap: 1.25rem;
}
.site-header__inner > .site-nav { justify-self: end; }

.site-logo {
  display: inline-flex;
  align-items: center;
  font-weight: 700;
  font-size: 1.05rem;
  letter-spacing: -0.01em;
  color: var(--color-fg);
  line-height: 0;
}
.site-logo__img {
  height: 28px;
  width: auto;
  display: block;
}
.site-logo:hover .site-logo__img { opacity: 0.8; }

.site-nav {
  display: flex;
  align-items: center;
  gap: 1.25rem;
}
.site-nav a {
  color: var(--color-fg);
  font-size: 0.9rem;
  font-weight: 500;
}
.site-nav a:hover                { color: var(--color-accent); }
.site-nav a[aria-current="page"] { color: var(--color-accent); }

/* --- mobile hamburger (hidden by default; toggled at <= 720px) --- */
.nav-toggle {
  display: none;
  appearance: none;
  background: transparent;
  border: 0;
  padding: 0.6rem 0.5rem;
  cursor: pointer;
  width: 2.5rem;
  height: 2.5rem;
  flex-direction: column;
  justify-content: space-between;
  align-items: stretch;
  color: var(--color-fg);
}
.nav-toggle__bar {
  display: block;
  height: 2px;
  background: currentColor;
  border-radius: 2px;
  transform-origin: center;
  transition: transform .2s ease, opacity .2s ease;
}
.nav-toggle[aria-expanded="true"] .nav-toggle__bar:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.nav-toggle[aria-expanded="true"] .nav-toggle__bar:nth-child(2) { opacity: 0; }
.nav-toggle[aria-expanded="true"] .nav-toggle__bar:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

@media (max-width: 720px) {
  .site-header__inner {
    grid-template-columns: auto minmax(0, 1fr) auto;
    grid-template-areas:
      "logo search toggle"
      "nav  nav    nav";
    gap: 0.5rem;
    row-gap: 0.5rem;
    padding-inline: 0.85rem;
  }
  .site-logo     { grid-area: logo; }
  .site-logo__img { height: 22px; } /* ~20% smaller than 28px */
  /* Search collapses to an icon-sized button on phones. Tapping it (focus)
     or typing a value expands the input to fill the row's leftover space.
     Magnifier stays visible on both states; the placeholder is hidden when
     collapsed so we don't ever flash "Search po…" through the icon. */
  .header-search {
    grid-area: search;
    width: 2.4rem;
    max-width: 100%;
    margin-inline: 0;
    justify-self: end;
    transition: width .25s ease;
  }
  .header-search .search input { padding-inline: 2rem; }
  .header-search .search__kbd  { display: none; }
  .header-search:focus-within,
  .header-search:has(input:not(:placeholder-shown)) {
    width: 100%;
  }
  /* Hide placeholder while collapsed so it doesn't ghost through the icon. */
  .header-search:not(:focus-within) input::placeholder { color: transparent; }
  .nav-toggle    { grid-area: toggle; display: flex; justify-self: end; }

  /* Nav becomes a stacked drawer collapsed by default — revealed when
     the hamburger has aria-expanded="true". */
  .site-nav {
    grid-area: nav;
    display: none;
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    border-top: 1px solid var(--color-rule);
    padding-block: 0.25rem;
    width: 100%;
  }
  .site-nav a {
    padding: 0.75rem 0.25rem;
    border-bottom: 1px solid var(--color-rule);
  }
  .site-nav a:last-child { border-bottom: 0; }
  .nav-toggle[aria-expanded="true"] + .site-nav { display: flex; }
}