实现元素宽度与高度一致

<style type="text/css">
#container {
width: 80%;
height: 500px;
}

.attr {
width: 100px;
height: 0;
padding-bottom: 50%;
background-color: #008b57;
}
</style>

<div id='container'>
<div class='attr'></div>
</div>