How to add buttons of sizes other than medium in navbar (and keep vertical alignment)?

Created by: niftylettuce

Code:

<li class="nav-item"><a class="btn btn-outline-secondary bg-inverse btn-sm">Support</a></li>
<li class="nav-item"><a class="btn btn-outline-secondary bg-inverse">Log in</a></li>
<li class="nav-item"><a class="btn btn-outline-secondary bg-inverse">Sign up</a></li>

Screenshot:

Expected output:

It should align vertically and doesn't. Not sure how to write it, couldn't find docs for this.

cc @mdo