/*美化返回顶部按钮，文字竖排，全部显示在圆内*/
.back-top{
	position:fixed;
	right:24px;
	bottom:40px;
	width:56px;
	height:56px;
	background-color:green;
	color:#ffffff;
	border-radius:50%;
	display:flex;
	justify-content:center;
	align-items:center;
	z-index:999;
	cursor:pointer;
	opacity:0;
	visibility:hidden;
	transition: all 0.3s cubic-bezier(0.4,0,0.2,1);
	font-size:13px;
	box-shadow: 0 4px 12px rgba(0,82,204,0.35);
	user-select:none;
	writing‑mode: vertical‑lr;
	letter‑spacing:2px;
}
.back-top.show{
	opacity:1;
	visibility:visible;
}
.back-top:hover{
	background-color:darkgreen;
	color:#fff;
	transform: translateY(-4px);
	box-shadow: 0 6px 16px rgba(0,82,204,0.45);
}
.back-top:active{
	transform: translateY(0);
}