lucy24 - 10:42 am on Jul 19, 2012 (gmt 0)
If headers aren't inside of something else with a defined size, then any relative size-- including percentages-- will be relative to the user default.
It shouldn't be necessary to set a size for paragraphs at all. If there's one thing that really should be in the user's default size, it's your vanilla paragraph! That's why browsers let you set a default size in the first place.
Somewhere in the CSS documentation there's an explanation of what "inherit" means. Find it and read it. Slowly! :)
Quick edit: Yes, everything will zoom the same, no matter what words you used to set the size.