We have included select2 plugin for enhanced select options. select2 is free and open source plugin you can check it here
Add the plugin css before the atlas stylesheet as we have tuned it according to the scheme of our admin panel
<link rel="stylesheet" href="assets/vendor/select2/css/select2.min.css">
<script src="assets/vendor/select2/js/select2.full.min.js" type="text/javascript"></script>
<select class="form-control js-select2">
<option selected>Apple Pie</option>
<option>Cup Cake</option>
<option>Donut</option>
<option>Eclair</option>
<option>Froyo</option>
<option>GingerBread</option>
<option>HoneyComb</option>
<option>Ice Cream Sandwich</option>
<option>Jellybean</option>
<option>Kitkat</option>
<option>Lollipop</option>
<option>Marshmallow</option>
<option>Nougat</option>
<option>Oreo</option>
</select>
$(".js-select2").select2();
<select multiple class="form-control js-select2">
<option selected>Apple Pie</option>
<option>Cup Cake</option>
<option>Donut</option>
<option>Eclair</option>
<option>Froyo</option>
<option>GingerBread</option>
<option>HoneyComb</option>
<option>Ice Cream Sandwich</option>
<option>Jellybean</option>
<option>Kitkat</option>
<option>Lollipop</option>
<option>Marshmallow</option>
<option>Nougat</option>
<option>Oreo</option>
</select>