Keep a given aspect ratio for any content

aspect.htm

<style>
	.aspectWrapper {
		position: relative;
	}
	
	.aspectImg {
		display: block;
		height: auto;
		position: relative;
		width: 100%;
	}
	
	.aspectContent {
		height: 100%;
		left: 0;
		position: absolute;
		top: 0;
		width: 100%;
	}
</style>
<div class="aspectWrapper">
	<img class="aspectImg" src="5x4.blank.gif" alt />
	<div class="aspectContent">
		whatever
	</div>
</dib>