Font Sizes

WP is a wonderful creation. However, for some reason, the font sizes seem too large to me. (Even the fonts and spacing in this support forum seem large, compared with many other sites that I frequent.) I know that it is possible to edit the templates to adjust the font sizes. Are the modifications made in the css files or the php files? Is there a global setting anywhere to reduce the font size by one unit? (Please don’t suggest that I change the font size in my browser as that would be the fonts on other sites too small; plus, chaning Text Size in IE does not have an effect on the WP pages, on my computer.)