[SOLVED] When using ui-select with theme Bootstrap: how to make the select smaller?

When using ui-select with theme Bootstrap, the "select" looks the same size of a Bootstrap button, ie: btn btn-default

I want the select to look like a "btn-sm" button.

How can I do that? what classes should I modify?

A solution someone gave in the Github site of ui-select:

Wrap the directive in a div with form-group-sm, eg:

<div class='form-group-sm'><ui-select>...</ui-select></div>