Link to stylesheet NOT in header.php

In theme BirdTIPS the there is no link to the stylesheet (style.css) in the header.php file. How do I link to this stylesheet and a custom stylesheet. (I’ve read a lot about linking to a custom stylesheet and if I can see how the link is created to the regular style.css sheet, I think I can figure out how to link to the custom one.) My site is natalbraziltourism.com.
Thanks.
Randy