Fix scrollbar being cut off at end of gutter
Summary:
The "mlb" on the left nav creates a phantom bottom margin which gives the content measurable height but not scrollable height. Replace it with "plb" (padding) instead.
The 2px-spacer calculation was also not quite correct.
Test Plan:
- Viewed pages with navs; padding vs margin didn't seem to make any other differences.
- Scrollbar now stops in the right place in Safari, Chrome, Firefox.
Reviewers: btrahan, chad
Reviewed By: chad
Subscribers: epriestley
Differential Revision: https://secure.phabricator.com/D12007