Jquery css() method
<html>
<head>
<title>Jquery set width</title>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
</head>
<body>
<h1>Jquery set width</h1>
<div id="d" style="border: 1px solid #ccc;height: 200px"></div>
<br>
<br>
<button id="b">Set Width</button>
<script>
$('#b').click(function() {
$('#d').css('width', '50%');
});
</script>
</body>
</html>