#scrollToTopBtn {
    position: fixed;
    left: 20px;
    bottom: 20px;
    display: none;
    align-items: center;
    justify-content: center;
    width: 58px;
    height: 58px;
    border-radius: 999px;
    background: var(--surface-strong);
    color: var(--text);
    border: 1px solid var(--line);
    box-shadow: var(--shadow-soft);
    opacity: 0;
    visibility: hidden;
    z-index: 21;
    transition: opacity 0.25s ease, transform 0.25s ease, box-shadow 0.25s ease;
}

#scrollToTopBtn:hover {
    transform: translateY(-3px);
    box-shadow: var(--shadow-card);
}

#scrollToTopBtn.visible {
    display: inline-flex;
    opacity: 1;
    visibility: visible;
}

#scrollToTopBtn.scrolling-up {
    transform: translateY(-14px);
    opacity: 0;
}

@media (max-width: 640px) {
    #scrollToTopBtn {
        width: 52px;
        height: 52px;
        left: 14px;
        bottom: 14px;
    }
}