Here is the proper code. Fix as needed. It keeps the cover aspect ratio correct.
Code:
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:ops="http://www.idpf.org/2007/ops" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<head>
<title>Ready Player One</title>
<link href="Clin_9780307887450_epub_css_r1.css" rel="stylesheet" type="text/css"/>
<meta content="application/xhtml+xml; charset=utf-8" http-equiv="Content-Type"/>
</head>
<body style="margin-top: 0px; margin-left: 0px; margin-right: 0px; margin-bottom: 0px; text-align: center;">
<div class="cover">
<img alt="" src="images/Clin_9780307887450_epub_cvi_r1.jpg" height="100%"/>
</div>
</body>
</html>
and in the CSS...
Code:
div.cover {
text-align: center
}