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<!DOCTYPE html>
<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.7.1/jquery.min.js"></script>
<script>
$(document).ready(function(){
  $("p").add(document.getElementsByTagName("span")[0]).css("background-color", "yellow");
});
</script>
</head>
<body>
<p>A p element.</p>
<p>Another p element.</p>
<span>A span element.</span>
<span>A span element.</span><br><br>
<div>This example adds the same css style for the first span element (index 0), as the existing p elements.</div>
</body>
</html>