.back-to-top {
    display: none;
    width: 40px;
    height: 40px;
    line-height: 40px;
    text-align: center;
    font-size: 26px;
    color: #fff;
    position: fixed;
    border-radius: 10px;
    bottom: 20px;
    right: 20px;
    background-color: rgba(0, 0, 0, 0.5);
    z-index: 5;
    transition: all 0.5s;
}

    .back-to-top:hover {
        background-color: #000;
        color: #fff;
    }

@media (prefers-color-scheme: light) {
    .back-to-top {
        background-color: rgba(0, 0, 0, 0.5);
        color: #fff;
        box-shadow: 0 2px 6px rgba(0,0,0,0.3);
    }
}

@media (prefers-color-scheme: dark) {
    .back-to-top {
        background-color: rgb(255 255 255 / 25%);
        color: #000;
        box-shadow: 0 2px 6px rgba(0,0,0,0.3);
    }
}