This is a minimized version of Semantic 'dropdown' only with optimum size, you can see samples here: https://semantic-ui.com/modules/dropdown.html
<head>
<link rel="stylesheet" href="dropdown.min.css">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script src="dropdown.min.js"></script>
</head>
<body>
<select name="selection[]" multiple="" class="ui dropdown">
<option value="option1">option1</option>
<option value="option2">option2</option>
<option value="option3">option3</option>
</select>
<script>
$('.dropdown').dropdown();
</script>
</body>
For more example and usage please visit UI Docs.
If you're looking for the full version of Semantic including all components and build tools check out the main project repository