yes, as bob_w has reminded me this does cause some concern on some browsers. there are also a variety of different size types you can choose from. a few examples i have listed below. but as a general rule i try to make pages that are compatible with the most common browsers used. as much as we would like, you can't make em all happy.
some examples would be: [color=#0000CC]cm, em, ex, in, pc, pt, px[/color]
the ones that are bolded are the common ones used. if all else fails just leave off the extension, the ones above, and just enter a number in the [color=#CC0000]font-size: ##;[/color] style command and it will work as the regular [color=#CC0000]##" >[/color] command.
there are many other combinations and styles to format your page to adapt to other browsers. i would highly recommend actually looking into the css scripting and get a general idea of everything it offers. i'm just throwing out the general basics.
“To learn all good things would be to learn nothing has value.” -Galious