font-size attribute in Opera Browser

Usually the developers use the attribute font-size in CSS specifying the font size in px, pt or em, for example. Most of them don't know it doesn't work in Opera... So, you need to have in mind that Opera follows the W3C specifications and, as it's true, if you are trying to change de font-size attribute for Opera Browser without success, you can see how to do this by visiting this website or just by taking a look at the following image:

I really think it helps in the standardization for the use of the fonts... I'm not telling that I like it, because it forbides us to make hacks, but we must try to do the things ok, right?