/* ===== back-to-top.css ===== */
.back-to-top {
    position: fixed;
    bottom: 70px;
    right: var(--spacing-lg);
    width: 44px;
    height: 44px;
    background-color: var(--color-primary);
    color: white;
    border: none;
    border-radius: var(--radius-full);
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    opacity: 0;
    visibility: hidden;
    transition: opacity var(--animation-speed-normal) ease, visibility var(--animation-speed-normal) ease, background-color var(--animation-speed-normal) ease, transform var(--animation-speed-normal) ease;
    z-index: 99;
    box-shadow: var(--shadow-sm);
    border: 1px solid rgba(255, 255, 255, 0.2);
}
.back-to-top.visible {
    opacity: 1;
    visibility: visible;
}
.back-to-top:hover {
    background-color: var(--color-secondary);
    transform: translateY(-2px);
}
.back-to-top i {
    font-size: var(--font-size-xl);
}