A commenter by the name of Moof in this thread leaves the code to make an RSS button (XML) completely in CSS:

<span style=”font-size: 10px; border: 0.4ex solid; border-color: #FC9 #630 #330 #F96; padding: 0 3px; font-face: sans-serif; font-weight: bold; color: #FFF; background: #F60; text-decoration: none;>XML</span>