<style>
span.wrap{
display:inline-block;
background-color:#EDE25D;
}
</style>
<p>asdasdasdasd 305 asdasdasdasd </p>
<script type="text/javascript">
var Find = '305';
var Replac = '<span class=wrap>'+Find+'</span>';
var h = document.body;
h.innerHTML = h.innerHTML.replace(eval("/"+Find+"/g"), Replac);
</script>