Are there any practical reasons to use “em” instead of “pt” font size units?

Question

One CSS rule I have learned is that you should use the relative \"em\" font-size unit instead of the absolute \"pt\". The general idea is to set the font-size in your body t

Answer 1

Depending on the country where you live, you might actually end up breaking the law using pt instead of em, depending on how hard your legislature want to enforce rules. Here in the UK, there is a disability discrimination act, which has been used to target companies where their websites have been rendered in a fixed font. This is treated as discrimination because it disadvantages the partially sited who may have increased their browser font sizes to compensate - but your site still renders fonts at the size you set, and not at the size they would expect.

Yes, it's harder to get to grips with relative font-sizes and fluid layouts, but if you want to comply with legislation, you have to take the time to get to grips with this.

For local government work in the UK, targets have been set to ensure that websites follow Double A guidelines, one of which states "Use relative rather than absolute units in markup language attribute values and style sheet property values". See here.