.site-header {
  position: sticky;
  top: 0;
  width: 100%;
  background-color: var(--color-header, #2b2f38);
  z-index: 1000;
  transition: box-shadow var(--transition-normal, 0.3s ease), background-color var(--transition-normal, 0.3s ease), opacity 0.15s ease;
  border-bottom: 1px solid var(--color-header-border, rgba(26, 26, 46, 0.1));
  opacity: 0;
}

.site-header.i18n-ready {
  opacity: 1;
}

.site-header.sticky {
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.25);
}

.header-inner {
  display: flex;
  justify-content: space-between;
  align-items: center;
  height: 70px;
}

.logo {
  display: flex;
  align-items: center;
  text-decoration: none;
  flex-shrink: 0;
}

.logo .logo-img {
  height: 40px;
  width: auto;
  display: block;
}

.brand-name {
  display: flex;
  flex-direction: column;
  margin-left: var(--space-sm, 8px);
  line-height: 1.15;
}

.brand-name .brand-zh {
  font-size: var(--font-size-lg, 18px);
  font-weight: 700;
  color: var(--color-header-text, #1a1a2e);
}

.brand-name .brand-en {
  font-size: var(--font-size-xs, 12px);
  font-weight: 500;
  letter-spacing: 1px;
  color: var(--color-header-text-muted, rgba(26, 26, 46, 0.65));
  text-transform: uppercase;
}

.main-nav {
  margin: 0 var(--space-xl, 48px);
}

.nav-list {
  display: flex;
  align-items: center;
  gap: var(--space-lg, 24px);
  list-style: none;
  margin: 0;
  padding: 0;
}

.nav-list a {
  font-size: var(--font-size-base, 16px);
  font-weight: 500;
  color: var(--color-header-text-muted, rgba(26, 26, 46, 0.65));
  text-decoration: none;
  transition: color var(--transition-fast, 0.2s ease);
  padding: var(--space-xs, 4px) 0;
  position: relative;
  white-space: nowrap;
}

.nav-list a:hover {
  color: var(--color-header-text, #1a1a2e);
}

.nav-list a::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 0;
  height: 2px;
  background-color: var(--color-accent, #00b4d8);
  transition: width var(--transition-fast, 0.2s ease);
}

.nav-list a:hover::after {
  width: 100%;
}

.nav-list .active a {
  color: var(--color-header-text, #1a1a2e);
}

.nav-list .active a::after {
  width: 100%;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: var(--space-md, 16px);
  flex-shrink: 0;
}

.lang-switcher {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 44px;
  min-width: 56px;
  padding: 0 var(--space-sm, 8px);
  background-color: transparent;
  border: 1px solid var(--color-header-border, rgba(26, 26, 46, 0.1));
  border-radius: 12px;
  color: var(--color-header-text-muted, rgba(26, 26, 46, 0.65));
  font-size: var(--font-size-xs, 12px);
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition-fast, 0.2s ease);
}

.lang-switcher:hover {
  border-color: var(--color-accent, #00b4d8);
  color: var(--color-header-text, #1a1a2e);
  background-color: rgba(26, 26, 46, 0.06);
}

.header-search {
  display: flex;
  align-items: center;
  height: 40px;
  background-color: rgba(26, 26, 46, 0.05);
  border: 1px solid rgba(26, 26, 46, 0.12);
  border-radius: 10px;
  overflow: hidden;
  transition: border-color var(--transition-fast, 0.2s ease), background-color var(--transition-fast, 0.2s ease);
}

.header-search:focus-within {
  border-color: var(--color-accent, #00b4d8);
  background-color: rgba(26, 26, 46, 0.08);
}

.header-search input {
  width: 160px;
  height: 100%;
  padding: 0 var(--space-sm, 8px) 0 var(--space-md, 16px);
  border: none;
  background: transparent;
  color: var(--color-header-text, #1a1a2e);
  font-size: var(--font-size-sm, 14px);
  font-family: var(--font-family, sans-serif);
  outline: none;
}

.header-search input::placeholder {
  color: rgba(26, 26, 46, 0.45);
}

.header-search button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 100%;
  border: none;
  background: transparent;
  color: var(--color-header-text-muted, rgba(26, 26, 46, 0.65));
  cursor: pointer;
  transition: color var(--transition-fast, 0.2s ease);
}

.header-search button:hover {
  color: var(--color-header-text, #1a1a2e);
}

.header-search button svg {
  width: 18px;
  height: 18px;
}

.hamburger {
  display: none;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  width: 44px;
  height: 44px;
  background: transparent;
  border: none;
  cursor: pointer;
  padding: 0;
  z-index: 1005;
  position: relative;
}

.hamburger span {
  display: block;
  width: 22px;
  height: 2px;
  background-color: var(--color-header-text, #1a1a2e);
  transition: all var(--transition-normal, 0.3s ease);
  transform-origin: center;
  position: absolute;
  left: 50%;
  margin-left: -11px;
}

.hamburger span:nth-child(1) { top: 14px; }
.hamburger span:nth-child(2) { top: 21px; }
.hamburger span:nth-child(3) { top: 28px; }

.hamburger.active span:nth-child(1) {
  transform: rotate(45deg);
}

.hamburger.active span:nth-child(2) {
  opacity: 0;
  width: 0;
}

.hamburger.active span:nth-child(3) {
  transform: rotate(-45deg);
}

@media (max-width: 768px) {
  .hamburger {
    display: flex;
  }

  .main-nav {
    position: fixed;
    top: 70px;
    left: 0;
    margin: 0;
    width: 100%;
    height: calc(100vh - 70px);
    background-color: var(--color-header, #2b2f38);
    transform: translateY(-100%);
    opacity: 0;
    pointer-events: none;
    transition: transform var(--transition-normal, 0.3s ease), opacity var(--transition-normal, 0.3s ease);
    z-index: 999;
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.3);
    overflow-y: auto;
  }

  .main-nav.nav-open {
    transform: translateY(0);
    opacity: 1;
    pointer-events: auto;
  }

  .nav-list {
    flex-direction: column;
    align-items: stretch;
    justify-content: center;
    gap: var(--space-lg, 24px);
    padding: var(--space-xl, 48px) var(--space-md, 16px);
    width: 100%;
    height: 100%;
  }

  .nav-list li {
    width: 100%;
  }

  .nav-list a {
    font-size: var(--font-size-lg, 18px);
    width: 100%;
    text-align: center;
    padding: var(--space-md, 16px) 0;
    min-height: 48px;
    display: flex;
    align-items: center;
    justify-content: center;
  }

  .brand-name .brand-zh {
    font-size: var(--font-size-base, 16px);
  }

  .header-search {
    display: none;
  }
}