jQuery and css

HTML

<!DOCTYPE html>
<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<script>
$(document).ready(function(){
  $("button").click(function(){
    $("#div1").width(500).height(500);
  });
});
</script>
<style>
#div1 {
  height: 100px;
  width: 300px;
  padding: 10px;
  margin: 3px;
  border: 1px solid blue;
  background-color: lightblue;
}
</style>
</head>
<body>

<div id="div1"></div>
<br>

<button>Změň rozměr div</button>

</body>
</html>