#scroll-top-btn {
    position: fixed;
    bottom: 2rem;
    right: 2rem;
    width: 48px;
    height: 48px;
    border-radius: 50%;
    border: none;
    background: var(--wp--preset--color--primary, #1a1a1a);
    color: #fff;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    opacity: 0;
    visibility: hidden;
    transform: translateY(10px);
    transition: opacity .3s ease, transform .3s ease, visibility .3s;
    z-index: 999;
    box-shadow: 0 2px 8px rgba(0,0,0,.2);
}

#scroll-top-btn.is-visible {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

#scroll-top-btn:hover {
    background: var(--wp--preset--color--secondary, #333);
}

@media (max-width: 600px) {
    #scroll-top-btn {
        bottom: 1rem;
        right: 1rem;
        width: 42px;
        height: 42px;
    }
}