The HTML file

index

<div data-role="page"> 
    <div data-role="header">
        <a href="import.html" data-rel="back" data-direction="reverse" data-icon="arrow-l">Lorem ipsum</a>
        <h1>Title</h1>
    </div><!-- /header -->

    <div data-role="content">
        <p>Lorem ipsum</p>
        <p>
           <!-- <img class="boximage" src="images/screen_playlist_add.png" /> -->
        </p>
		<style type="text/css">
			@media all and (max-width: 800px) {
				.boximage {
					background: url(../images/gruenerHaken.jpg);
				}
			}
			@media all and (min-width: 800px) {
				.boximage {
					background: ulr(../images/screen_playlist_add.png);
				}
			}
		</style>
      </div>
</div>