What changes what text in themes?

[Steve]

Is there a guide somewhere that tells me where to go to change text sizes in various places in a theme?

And what the heck is 'em' and what does it and percentages do in relation to text sizes?

[Burke ♞ Knight]

Measurement Values
Unit    Description
%    percentage
in    inch
cm    centimeter
mm    millimeter

em    1em is equal to the current font size. 2em means 2 times the size of the current font. E.g., if an element is displayed with a font of 12 pt, then '2em' is 24 pt. The 'em' is a very useful unit in CSS, since it can adapt automatically to the font that the reader uses

ex    one ex is the x-height of a font (x-height is usually about half the font-size)
pt    point (1 pt is the same as 1/72 inch)
pc    pica (1 pc is the same as 12 points)
px    pixels (a dot on the computer screen)

[Kindred]

as for where to go...   CSS files.

What file and what reference in that file?   Well, I suggest getting firefox+firebug - or chrome webdev/inspect element.

[Steve]

Ah, thanks for that BK.

I totally forgot about using firebug. Will do that and thanks for the reminder Kindred.

[Hj Ahmad Rasyid Hj Ismail]

You can refer to this tip is you want Steve: http://www.simplemachines.org/community/index.php?topic=527506.msg3741301#msg3741301