.scrolltop-btn {
    position: fixed;
    right: 20px;
    bottom: 22px;
    z-index: 9999;

    width: 48px;
    height: 48px;
    display: grid;
    place-items: center;

    border: 0;
    border-radius: 999px;
    cursor: pointer;

    color: #fff;
    background: linear-gradient(135deg, var(--theme-primary, #047857), var(--theme-secondary, #065f46));
    box-shadow: 0 16px 35px rgba(15, 23, 42, .18);

    opacity: 0;
    visibility: hidden;
    transform: translateY(10px);
    transition: all .25s ease;
}

.scrolltop-btn.is-show {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

.scrolltop-btn:hover {
    transform: translateY(-4px);
}

@media (max-width: 640px) {
    .scrolltop-btn {
        right: 14px;
        bottom: 16px;
        width: 44px;
        height: 44px;
    }
}