html - Which unit I should use in CSS when designing a web page

Question

I have designed and developed more than 10 sites, but I still have a doubt about the correct unit I should use. Should it be px, em or %?

EDIT 1: FOR LAYOUTS (Especially for container boxes)

Answer 1

Different units depending on context. If there was one that was best for every situation, then there wouldn't be so many units.

As rules of thumb go:

If you are working on screen media:

• Use % for font sizes
• Use px for images
• Use px, %, or em for box sizes
• Use ratios for line height

If you are working in print media:

• It might be wise to avoid px (this is not a hard rule by any means) and everything else is fair game. It really depends how much control you want.