/* Back to top button */
.back-to-top {
    position: fixed;
    bottom: 2em;
    right: 2em;
    width: 42px;
    height: 42px;
    border-radius: 50%;
    background: var(--sidebar-active-bg, #f0f0f0);
    color: var(--fg, #333);
    border: 1px solid var(--sidebar-bg, #ddd);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 20px;
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.3s, visibility 0.3s;
    z-index: 999;
    box-shadow: 0 2px 8px rgba(0,0,0,0.15);
}

.back-to-top:hover {
    background: var(--sidebar-active-bg, #e0e0e0);
    transform: translateY(-2px);
}

.back-to-top.visible {
    opacity: 1;
    visibility: visible;
}