.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: color-mix(in oklab, var(--bg) 85%, transparent);
  -webkit-backdrop-filter: saturate(160%) blur(14px);
  backdrop-filter: saturate(160%) blur(14px);
  border-bottom: 1px solid transparent;
  transition: border-color var(--dur), background var(--dur);
}
.site-header.is-scrolled {
  border-bottom-color: var(--border);
  background: color-mix(in oklab, var(--bg) 92%, transparent);
}

.header-inner {
  display: flex;
  align-items: center;
  gap: 20px;
  height: 72px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  font-family: "Space Grotesk", sans-serif;
  font-weight: 800;
  font-size: 1.25rem;
  color: var(--text);
  letter-spacing: -0.01em;
}
.brand:hover { color: var(--text); }
.brand-mark { border-radius: 10px; }
.brand-accent {
  background: var(--brand-grad);
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}

.nav { margin-left: 32px; flex: 1; }
.nav-list {
  display: flex;
  gap: 28px;
  list-style: none;
  margin: 0;
  padding: 0;
}
.nav-list a {
  position: relative;
  color: var(--text-muted);
  font-weight: 500;
  font-size: .95rem;
  padding: 6px 2px;
}
.nav-list a::after {
  content: "";
  position: absolute;
  left: 0; right: 0; bottom: -4px;
  height: 2px;
  background: var(--brand-grad);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform var(--dur) var(--ease-out);
}
.nav-list a:hover { color: var(--text); }
.nav-list a:hover::after { transform: scaleX(1); }

.header-actions {
  display: flex;
  align-items: center;
  gap: 10px;
}
.btn-sm { padding: 8px 16px; font-size: .85rem; }

.lang-select { position: relative; }
.lang-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 8px 12px;
  background: var(--surface);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 999px;
  font-weight: 600;
  font-size: .85rem;
  cursor: pointer;
  transition: background var(--dur-fast);
}
.lang-btn:hover { background: var(--surface-hover); }
.lang-menu {
  position: absolute;
  top: calc(100% + 8px);
  right: 0;
  min-width: 160px;
  background: var(--bg-elev);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 6px;
  list-style: none;
  margin: 0;
  box-shadow: var(--shadow);
  opacity: 0;
  transform: translateY(-8px) scale(.98);
  pointer-events: none;
  transition: opacity var(--dur-fast), transform var(--dur-fast);
  z-index: 60;
}
.lang-menu.is-open {
  opacity: 1;
  transform: none;
  pointer-events: auto;
}
.lang-menu li {
  padding: 8px 12px;
  border-radius: 8px;
  cursor: pointer;
  font-size: .9rem;
  color: var(--text-muted);
  transition: background var(--dur-fast), color var(--dur-fast);
}
.lang-menu li:hover { background: var(--surface-hover); color: var(--text); }

.theme-toggle {
  width: 38px; height: 38px;
  border-radius: 50%;
  background: var(--surface);
  border: 1px solid var(--border);
  color: var(--text);
  cursor: pointer;
  display: grid;
  place-items: center;
  position: relative;
  transition: background var(--dur-fast), transform var(--dur-fast);
}
.theme-toggle:hover { background: var(--surface-hover); transform: rotate(12deg); }
.theme-toggle svg {
  position: absolute;
  transition: opacity var(--dur) var(--ease-out), transform var(--dur) var(--ease-out);
}
html[data-theme="dark"] .icon-sun { opacity: 1; transform: rotate(0); }
html[data-theme="dark"] .icon-moon { opacity: 0; transform: rotate(-90deg) scale(.5); }
html[data-theme="light"] .icon-sun { opacity: 0; transform: rotate(90deg) scale(.5); }
html[data-theme="light"] .icon-moon { opacity: 1; transform: rotate(0); }

.menu-toggle {
  display: none;
  width: 40px; height: 40px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  cursor: pointer;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 4px;
  padding: 0;
}
.menu-toggle span {
  width: 18px; height: 2px;
  background: var(--text);
  border-radius: 2px;
  transition: transform var(--dur), opacity var(--dur);
}
.menu-toggle[aria-expanded="true"] span:nth-child(1) { transform: translateY(6px) rotate(45deg); }
.menu-toggle[aria-expanded="true"] span:nth-child(2) { opacity: 0; }
.menu-toggle[aria-expanded="true"] span:nth-child(3) { transform: translateY(-6px) rotate(-45deg); }

@media (max-width: 960px) {
  .nav {
    position: fixed;
    top: 72px; left: 0; right: 0;
    background: var(--bg-elev);
    border-bottom: 1px solid var(--border);
    padding: 24px;
    margin: 0;
    transform: translateY(-110%);
    transition: transform var(--dur) var(--ease-out);
    z-index: 40;
  }
  .nav.is-open { transform: none; }
  .nav-list {
    flex-direction: column;
    gap: 18px;
  }
  .nav-list a { font-size: 1.05rem; }
  .menu-toggle { display: flex; }
  .btn-ghost.btn-sm, .lang-select { display: none; }
}
@media (max-width: 540px) {
  .btn-primary.btn-sm { display: none; }
}