github地址:
https://github.com/echoorx/opacity-Gradient
zindex好像不能渐变改变，所以用opcity来模拟
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
div{
width: 100px;
height: 100px;
position: absolute;
top: 0;
}
.big{
background-color: red;
}
.small{
background-color: green;
z-index: 1;
opacity: 0;
}
#btn{
margin-top: 200px;
}
</style>
</head>
<div class="big"></div>
<div class="small"></div>
<input id="btn" value="1111" type="button">
<body>
<script>
var btn = document.querySelector('#btn');
var small = document.querySelector('.small')
btn.addEventListener('click',function(){
var timer = setInterval(function(){
var opc = window.getComputedStyle(small, null)["opacity"];
opc = opc * 100 + 2;
opc /= 100;
small.style.opacity = opc;
if(opc == 1){
clearInterval(timer)
}
},10)
})
</script>
</body>
</html>