jQuery css()

 
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>jQuery css()</title>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" />
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script>
$(document).ready(function() {
  $("#button").click(function() {
     alert("Font Size is : " + $("p").css("font-size"));
  });
});
</script>
</head>
<body>
 <p style="font-size:18px">lorem ipsum dolor sit</p>
 <button style="margin:0 0 10px 0;background:#e8e8e8;" class="btn" id="button">Click here to get a font size of first matched element</button><br />
 </body>
</html>                            