.header-region {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: 54px;
    z-index: var(--theme-z-sticky);
}

.header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 54px;
    padding: 0 14px;
    gap: 12px;
    background: var(--theme-surface-raised);
    border-bottom: 1px solid var(--theme-border-subtle);
    box-shadow: var(--theme-shadow-sm);
    transform: translateY(-100%);
    transition: transform 220ms ease;
}

.header-region:hover .header,
.chrome-pinned .header {
    transform: translateY(0);
}

.header-group {
    display: flex;
    align-items: center;
    gap: 2px;
    flex: 0 0 auto;
}

.header-title {
    flex: 1;
    text-align: center;
    font-family: var(--theme-font-sans);
    font-size: var(--theme-font-sm);
    font-weight: var(--theme-font-weight-semibold);
    color: var(--theme-text-secondary);
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.header-btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 38px;
    height: 38px;
    border: none;
    border-radius: var(--theme-radius-sm);
    background: none;
    cursor: pointer;
    color: var(--theme-text-secondary);
    transition: background 150ms ease, color 150ms ease;
}

.header-btn:hover {
    background: var(--theme-bg-secondary);
    color: var(--theme-text-primary);
}

.header-btn.is-active {
    color: var(--theme-text-primary);
}

@media (max-width: 640px) {
    .header-btn { width: 34px; height: 34px; }
    .header-title { display: none; }
}