Tutorial: how to attach an image to a link in css

First I made an unordered list in my html body with two links that I wanted. Here's an example below.

<div>
<ul>
	<li id="girl">
		<a href="http://looliwun.com">looliwun</a>
		</li>
	<li id="boy">
		<a href="http://hungred.com">hungred</a>
		</li>
		</ul>
</div>

This would result in a basic unordered list.