How do I add a src in style class?

<div><img class="imgClose"></div>
 

I tried adding like this, but it does not show the image:

<style type="text/css">
 .imgClose
 {
    float: right;
    margin-top: -15px;
    background: 16px 16px no-repeat url(_assets/img/close.png);
 }
 </style>
 

If I add in the HTML, then it works, but I would like to put the src in style class instead.

<div><img class="imgClose" src="_assets/img/close.png"></div>
 

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