css图片宽高相等设置

<style>
	.image-header{
		position:relative;
		width:100%;
		height:0;
		padding-top:100%;
	}
	.image-header img{
		position:absolute;
		top:0;
		left:0;
		width:100%;
		height:100%;
	}
</style>
<div class="image-header">
	<img src="demo.jpg">
</div>