/* 站点顶栏 */
.site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  height: var(--header-height);
  background: rgba(255, 255, 255, 0.85);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--color-border);
}

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

.brand {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  font-weight: 400;
  font-size: 1.15rem;
  color: var(--color-text);
}

.brand:hover {
  color: var(--color-primary-dark);
}

.site-header .brand-logo {
  display: block;
  flex-shrink: 0;
  width: 32px;
  height: 32px;
  max-width: 32px;
  max-height: 32px;
  object-fit: contain;
  background: none;
  border: none;
  border-radius: 0;
  box-shadow: none;
}

.brand-icon {
  width: 36px;
  height: 36px;
  display: grid;
  place-items: center;
  background: linear-gradient(135deg, var(--color-primary), var(--color-primary-dark));
  color: white;
  border-radius: var(--radius-sm);
  font-family: var(--font-display);
  font-size: 1.1rem;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 0.25rem;
  list-style: none;
  margin: 0;
  padding: 0;
}

.nav-links a {
  padding: 0.5rem 0.85rem;
  border-radius: var(--radius-sm);
  color: var(--color-text-secondary);
  font-size: 0.95rem;
}

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

.nav-actions {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.nav-actions .btn-primary {
  background: var(--color-primary-ghost);
  color: var(--color-primary-dark);
  border: none;
  box-shadow: none;
}

.nav-actions .btn-primary:hover {
  background: var(--color-primary-ghost);
  color: var(--color-primary-dark);
  transform: none;
  box-shadow: none;
}

/* 按钮 */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.4rem;
  padding: 0.55rem 1.15rem;
  font-size: 0.95rem;
  font-weight: 500;
  font-family: inherit;
  border: none;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all var(--transition);
  text-decoration: none;
}

.btn-primary {
  background: linear-gradient(
    135deg,
    var(--color-primary),
    var(--color-primary-dark)
  );
  color: var(--color-text-inverse);
  box-shadow: var(--shadow-sm);
}

.btn-primary:hover {
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
  color: white;
}

.btn-outline {
  background: transparent;
  color: var(--color-primary-dark);
  border: 1.5px solid var(--color-border-strong);
}

.btn-outline:hover {
  background: var(--color-primary-pale);
  border-color: var(--color-primary);
}

.btn-ghost {
  background: transparent;
  color: var(--color-text-secondary);
}

.btn-ghost:hover {
  background: var(--color-primary-ghost);
  color: var(--color-primary-dark);
}

.btn-lg {
  padding: 0.75rem 1.5rem;
  font-size: 1rem;
  border-radius: var(--radius-md);
}

.btn-block {
  width: 100%;
}

.btn:disabled {
  opacity: 0.55;
  cursor: not-allowed;
  transform: none;
}

/* 卡片 */
.card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  box-shadow: var(--shadow-sm);
  transition:
    box-shadow var(--transition),
    transform var(--transition);
}

.card:hover {
  box-shadow: var(--shadow-md);
}

.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1.25rem;
}

/* 表单 */
.form-group {
  margin-bottom: 1.25rem;
}

.form-group label {
  display: block;
  margin-bottom: 0.4rem;
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--color-text-secondary);
}

.form-input {
  width: 100%;
  padding: 0.65rem 0.9rem;
  font-size: 1rem;
  font-family: inherit;
  border: 1.5px solid var(--color-border);
  border-radius: var(--radius-sm);
  background: var(--color-bg-elevated);
  color: var(--color-text);
  transition:
    border-color var(--transition),
    box-shadow var(--transition);
}

.form-input:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px var(--color-primary-ghost);
}

.form-hint {
  margin-top: 0.35rem;
  font-size: 0.85rem;
  color: var(--color-text-muted);
}

.form-error {
  margin-top: 0.5rem;
  padding: 0.6rem 0.85rem;
  font-size: 0.9rem;
  color: var(--color-danger);
  background: rgba(212, 93, 93, 0.08);
  border-radius: var(--radius-sm);
  display: none;
}

.form-error.visible {
  display: block;
}

/* 徽章 */
.badge {
  display: inline-block;
  padding: 0.2rem 0.55rem;
  font-size: 0.75rem;
  font-weight: 600;
  border-radius: var(--radius-full);
  background: var(--color-primary-pale);
  color: var(--color-primary-darker);
}

.badge-level {
  background: var(--color-primary-ghost);
}

/* 页脚 */
.site-footer {
  padding: 2.5rem 0;
  border-top: 1px solid var(--color-border);
  background: var(--color-bg-elevated);
  color: var(--color-text-muted);
  font-size: 0.9rem;
  text-align: center;
}

/* 数学内容区 */
.math-content {
  font-size: 1.05rem;
  line-height: 1.75;
}

.math-content .placeholder {
  padding: 2rem;
  text-align: center;
  color: var(--color-text-muted);
  background: var(--color-primary-pale);
  border-radius: var(--radius-md);
  border: 1px dashed var(--color-border-strong);
}

.math-content pre {
  overflow-x: auto;
  padding: 1rem;
  background: #f0f4fa;
  border-radius: var(--radius-sm);
}

/* 加载与空状态 */
.loading-spinner {
  width: 40px;
  height: 40px;
  border: 3px solid var(--color-border);
  border-top-color: var(--color-primary);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
  margin: 2rem auto;
}

@keyframes spin {
  to {
    transform: rotate(360deg);
  }
}

.empty-state {
  text-align: center;
  padding: 3rem 1.5rem;
  color: var(--color-text-muted);
}

.btn-sm {
  padding: 0.4rem 0.85rem;
  font-size: 0.85rem;
}

/* 用户菜单 */
.user-chip {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  padding: 0.2rem 0.55rem 0.2rem 0.2rem;
  border-radius: var(--radius-full);
  background: transparent;
  border: 1px solid var(--color-border);
  font-size: 0.88rem;
  color: inherit;
  text-decoration: none;
  transition:
    border-color var(--transition),
    box-shadow var(--transition),
    transform var(--transition);
}

.user-chip:hover {
  border-color: var(--color-primary-light);
  box-shadow: var(--shadow-sm);
  transform: translateY(-1px);
}

.user-chip.is-active {
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px var(--color-primary-ghost);
}

.user-chip-text {
  display: flex;
  flex-direction: column;
  line-height: 1.15;
  min-width: 0;
}

.user-chip-name {
  font-weight: 600;
  font-size: 0.82rem;
  color: var(--color-text);
  max-width: 7rem;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.user-chip-id {
  font-family: var(--font-mono);
  font-size: 0.68rem;
  font-variant-numeric: tabular-nums;
  color: var(--color-text-muted);
}

.user-chip-chevron {
  font-size: 1rem;
  line-height: 1;
  color: var(--color-text-muted);
  margin-left: 0.1rem;
  transition: transform var(--transition);
}

.user-chip:hover .user-chip-chevron {
  transform: translateX(2px);
  color: var(--color-primary-dark);
}

.user-avatar {
  width: 28px;
  height: 28px;
  border-radius: 50%;
  background: var(--color-primary);
  color: white;
  display: grid;
  place-items: center;
  font-size: 0.8rem;
  font-weight: 600;
}

@media (max-width: 768px) {
  .nav-links {
    display: none;
  }

  .nav-links.mobile-open {
    display: flex;
    flex-direction: column;
    position: absolute;
    top: var(--header-height);
    left: 0;
    right: 0;
    padding: 1rem;
    background: white;
    border-bottom: 1px solid var(--color-border);
    box-shadow: var(--shadow-md);
  }

  .nav-toggle {
    display: inline-flex;
  }
}

@media (min-width: 769px) {
  .nav-toggle {
    display: none;
  }
}