.to-top {
    position: fixed;
    right: 1rem;
    bottom: 1rem;
    width: 8rem; 
    height: 8rem;
    background: url(../assets/img/Back_To_The_Top.png) no-repeat center/contain;
    border: none;
    background-size: contain; /* 見た目は縦横比維持 */
    cursor: pointer;
    transition: opacity 0.3s ease;
    z-index: 9999;
}

.to-top:hover {
    opacity: 0.6;
}

/* PC向けにサイズを大きく調整 */
@media(min-width: 1024px) {
    .to-top {
        width: 13rem;
        height: 13rem;
        background-size: 14rem 14rem;
    }
}