<style>
.box{
position:fixed;
right:10px;
bottom: 10px;
height:30px;
width: 50px;
text-align:center;
padding-top:20px;
background-color: lightblue;
border-radius: 20%;
overflow: hidden;
}
.box:hover:before{
top:50%
}
.box:hover .box-in{
visibility: hidden;
}
.box:before{
position: absolute;
top: -50%;
left: 50%;
transform: translate(-50%,-50%);
content:'回到顶部';
width: 40px;
color:peru;
font-weight:bold;
}
.box-in{
visibility: visible;
display:inline-block;
height:20px;
width: 20px;
border: 3px solid black;
border-color: white transparent transparent white;
transform:rotate(45deg);
}
</style>
<body style="height:2000px;">
<div id="box" class="box">
<div class="box-in"></div>
</div>
</body>
<script>
var timer = null;
box.onclick = function(){
cancelAnimationFrame(timer);
timer = requestAnimationFrame(function fn(){
var oTop = document.body.scrollTop || document.documentElement.scrollTop;
if(oTop > 0){
document.body.scrollTop = document.documentElement.scrollTop = oTop - 50;
timer = requestAnimationFrame(fn);
}else{
cancelAnimationFrame(timer);
}
});
}
</script>