Should I use percentage if I want to change size of forum-wide font?

[Arskrigitsioniets]

In basic css from standard theme Curve2 I see .body font-size style indicated in percentage. But where is the root element, percentage of which is used? Or it's more correctly to edit this percentage if I want to change the font size?

[Sesquipedalian]

The default font size that all browsers start with is 16px. If relative font sizes traced up through the CSS inheritance tree reach the root element without encountering an absolute value, that's the value that will be used as the base.