Typically most browsers are set to use 12pt as the default size but this varies with browser, personal preferences and platform. In addition, screen display sizes of fonts are approximately 3 point sizes larger on PC machines. What this means is that when you view the same site on a PC browser and on a Macintosh browser, and both browsers have their default font size set to 12pt Times, the actual space which each character takes up is larger on the PC than on the Mac. Thus when designing web pages it is very important to test your design across different browser versions and platforms to make sure that the design is looking the way you want. Typically no two browsers or platforms display a page exactly the same, and one of the things which is difficult, especially when coming from a print media background, is to realize that the fonts are not going to look exactly the same everywhere.
Designs have to be flexible to accommodate changing elements.
CSS and Layers helps a lot in this department because it can fix the location of elements within the page. However, we do not currently generate anything which can control the font sizes though there are scripts you can use under the CSS specifications which can do this under some browsers. These scripts can be added to pages using our coding interface, so if that ever is required by one of your designs, it can be done through that method. What many web designers do is that if they want text to use a particular font or remain unchanged through browser translation, they make an image of that text, such as a gif, and use that in place of text elements.