Improve visibility of smallest font elements

Problem/Motivation

The Bartik theme sets its base font size to 87.5% for the body. The end result are pages with font sizes ranging from 12px to 24px. For most content the font size is smaller than my browser's default (15px for the main content, 12.8px in the sidebar, 12px in the footer).
I have aging eyes. Therefore I set the default font size in my browser to higher than the common default of 16px, which sometimes breaks form layouts. Or I have to use the browsers zoom feature, a blunt tool that can be more annoying than helpful, and one that many don't know exists.

Proposed resolution

• For body, set font-size:100% to honor users' browser preferences
• For all other selectors, modify font size as needed to maintain form structure and text size balance across a page, but never hide content from low vision users by using a font size that's less than 1em.

I believe in stylistic choice and won't recommend this for all themes, but since Bartik is the default theme, I feel strongly that everyone should be able to see its content without having to know the browser zoom keystrokes (some users aren't aware of these).