Hi zzz,
Refer the below article.
Also created below Sample using select2 plugin.
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/css/select2.min.css" />
<script src="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/js/select2.min.js"></script>
<script type="text/javascript">
$(function () {
$(".js-example-programmatic").select2({ placeholder: "Select a Product" });
});
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<select multiple style="width: 300px" class="js-example-programmatic">
<option value="Alice Mutton">Alice Mutton</option>
<option value="Aniseed Syrup">Aniseed Syrup</option>
<option value="Boston Crab Meat">Boston Crab Meat</option>
<option value="Camembert Pierrot">Camembert Pierrot</option>
<option value="Carnarvon Tigers">Carnarvon Tigers</option>
<option value="Chai">Chai</option>
<option value="Chang">Chang</option>
<option value="Chartreuse verte">Chartreuse verte</option>
</select>
</div>
</form>
</body>
</html>
Demo
