kolhoz,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<style type="text/css">
h3 > span{
background-color:#7CFC00;
}
</style>
<meta charset="utf-8">
<script>
window.addEventListener('DOMContentLoaded', function() {
[].forEach.call( document.querySelectorAll('.moduletable h3'), function(el) {
el.innerHTML = "<span>" + el.innerHTML + "<span/>"
});
});
</script>
</head>
<body>
<div class="moduletable">
<h3>Заголовок</h3>
Текст
</div>
</body>
</html>
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<style type="text/css">
h3 > span{
background-color:#7CFC00;
}
</style>
<meta charset="utf-8">
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.js"></script>
<script>
jQuery(function () {
$(".moduletable h3").wrapInner("<span/>")
});
</script>
</head>
<body>
<div class="moduletable">
<h3>Заголовок</h3>
Текст
</div>
</body>
</html>