Those icons are fonts. You will need to install the fontpack first to use them or extract the images from the fontpack and manipulate the size with CSS.
You can then use the CSS to add the icon in font notation
\f212 or as an image url("path to image") before the text that is currently in the tab using
content on the unique css selector for each tab.
http://www.w3.org/wiki/CSS/Properties/content