tweak CSS for pre+discussion

1. the edit mode is fixed (see example)

2. font-family is a skin-by-skin decision. default is fine for "classic" wagn look (I'll remove explicit monospace setting)

3. will remove font-size setting. default will go to 12px

4. re padding: yuck! text lines up against background. looks awful.

5. working on removing explicit line height settings wherever possible. should be better by default.