I put a padding of 30px, the select actually gets bigger but it does not appear anything.
select.custom{
padding: 30px!important;
-moz-appearance: none;
-webkit-appearance:none;
}
select.custom option{
padding: 30px!important;
-moz-appearance: none;
-webkit-appearance:none;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script><linkhref="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet"/>
<div class="col-md-12">
<select class="form-control custom">
<option>AAAAAAAAAAAAAA</option>
</select>
</div>