font sizes, css, and xhtml

Apparently my use of "\\\…" results in my page being invalid xhtml transitional. I am not sure why I care; the browsers render what I want. I do care however, so I am left in a bind. I do not know much about CSS, certainly not enough to have done more than trivially edit the WordPress theme I am using. From what I see in my search results, I am supposed to be using CSS to handle this sort of font sizing thing, and while I see something to that effect in the style.css for the theme, it appears to be wrapped up in how comments are treated. I really do not know what I am doing, and advice and/or assistance would be welcome, including a pointer to a Fine Manual for me to Read (reference to RTFM).

On the off chance that anyone is willing to look at it, the style.css is up at luke/style.txt.

UPDATE 2006-08-08 22:34 EDT: Vincas rocks. He pointed me at http://alistapart.com/articles/taminglists/ and then continued to help me with examples and letting me think out loud until I figured out enough to add my own div id stuff. So now I can make my references display small without violating xhmtl transitional. ☺