j0hnik,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script>
<script>
$(function(){
jQuery.expr[":"].contains = function( elem, i, match, array ) {
return (elem.textContent || elem.innerText || jQuery.text( elem ) || "") == match[3];
}
$('category:contains(1)').css({"font-size": "50px"})
});
</script>
</head>
<body>
<category>11</category>
<category>1</category>
<category>21</category>
</body>
</html>