/* back to top */
#backToTheTop {
	position: fixed;
	right: 5px;
	bottom: 5px;
	/* デフォルトは非表示 */
    opacity: 0;
    visibility: hidden;
    transition: 0.2s;
}

#backToTheTop.visible {
    opacity: 1;
    visibility: visible;
    z-index: 1;
}