/* ========================================
   TOP BAR — 普通文档流，随页面滚动消失
   ======================================== */
.top-bar {
  background: #0A0A0A;
  color: var(--text-primary);
  font-size: 12px;
  height: var(--top-bar-height);
  overflow: hidden;
  border-bottom: 1px solid var(--border-color);
}

.top-bar-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
}

.top-logo {
  color: var(--accent-primary);
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 13px;
  letter-spacing: 0.5px;
}

.top-logo:hover {
  color: var(--text-primary);
  text-decoration: none;
}

.utility-nav {
  display: flex;
  align-items: center;
  gap: var(--space-md);
}

.utility-nav ul {
  display: flex;
  gap: var(--space-lg);
}

.utility-nav ul li {
  list-style: none;
}

.utility-nav ul a {
  color: var(--accent-primary);
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.5px;
}

.utility-nav ul a:hover {
  color: var(--text-primary);
  text-decoration: underline;
}

/* ========================================
   MAIN NAVIGATION — sticky，吸附在顶部
   ======================================== */
.nav {
  position: sticky;
  top: 0;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background: var(--bg-card);
  border-bottom: 1px solid var(--border-color);
  z-index: 1000;
  transition: box-shadow var(--transition-normal);
}

.nav.scrolled {
  box-shadow: 0 2px 16px rgba(0, 0, 0, 0.3);
}

.nav-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-md);
}

.nav-logo {
  font-family: var(--font-display);
  font-size: 18px;
  font-weight: 700;
  color: var(--text-primary);
  letter-spacing: -0.3px;
  flex-shrink: 0;
}

.nav-logo:hover {
  color: var(--accent-primary);
}

.nav-links {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-sm);
  list-style: none;
  margin: 0;
  padding: 0;
  height: 100%;
  position: absolute;
  left: 50%;
  transform: translateX(-50%);
}

.nav-links li {
  display: flex;
  align-items: center;
  height: 100%;
}

.nav-links a {
  position: relative;
  color: var(--text-secondary);
  font-size: 0.95rem;
  font-weight: 500;
  padding: 0.5rem 0.75rem;
  transition: color var(--transition-fast);
  display: flex;
  align-items: center;
  height: 100%;
  letter-spacing: 0.3px;
}

.nav-links a::after {
  content: '';
  position: absolute;
  bottom: 8px;
  left: 50%;
  transform: translateX(-50%) scaleX(0);
  width: 60%;
  height: 2px;
  background: var(--accent-primary);
  border-radius: 1px;
  transition: transform var(--transition-fast);
  transform-origin: center;
}

.nav-links a:hover,
.nav-links a.active {
  color: var(--accent-primary);
  background: transparent;
}

.nav-links a:hover::after,
.nav-links a.active::after {
  transform: translateX(-50%) scaleX(1);
}

/* ===== 操作按钮（语言/主题切换） ===== */

.nav-actions {
  display: flex;
  align-items: center;
  gap: var(--space-xs);
  flex-shrink: 0;
}

.nav-action-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  padding: 0;
  background: transparent;
  border: none;
  border-radius: var(--radius-sm);
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.nav-action-btn:hover {
  color: var(--accent-primary);
  background: rgba(34, 197, 94, 0.05);
}

.nav-action-btn .lang-text {
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.5px;
}

.nav-action-btn svg {
  width: 18px;
  height: 18px;
}

.nav-action-btn .icon-moon {
  display: none;
}

[data-theme="dark"] .nav-action-btn .icon-sun {
  display: none;
}

[data-theme="dark"] .nav-action-btn .icon-moon {
  display: block;
}

/* 移动端适配 */
@media (max-width: 767px) {
  .top-bar {
    display: none;
  }

  .nav-links {
    gap: var(--space-xs);
  }

  .nav-links a {
    font-size: 0.85rem;
    padding: 0.5rem;
  }
}

@media (max-width: 480px) {
  .nav-logo {
    font-size: 14px;
  }

  .nav-links a {
    font-size: 0.8rem;
    padding: 0.4rem;
  }
}