You can use select2 . it is the best js for this job.
https://select2.org/dropdown
$(document).ready(function () {_x000D_
//change selectboxes to selectize mode to be searchable_x000D_
$("select").select2();_x000D_
});
_x000D_
<html>_x000D_
<head>_x000D_
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>_x000D_
<link href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/select2.min.css" rel="stylesheet" />_x000D_
<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/js/select2.min.js"></script>_x000D_
_x000D_
</head>_x000D_
<body>_x000D_
<select id="select_page" style="width:200px;" class="operator"> _x000D_
<option value="">Select a Page...</option>_x000D_
<option value="alpha">alpha</option> _x000D_
<option value="beta">beta</option>_x000D_
<option value="theta">theta</option>_x000D_
<option value="omega">omega</option>_x000D_
</select>_x000D_
</body>_x000D_
</html>
_x000D_