Scribble CSS fixes

Fixed two problems in new CSS for Scribble docs.

Both problems are visible [on this page](http://www.cs.utah.edu/plt/snapshots/current/doc/reference/notation.html).

+ In defmodule box, the left and right pieces of text do not align vertically because they're different sizes. Resolved by making them the same size.

+ Blue definition boxes on this page are intended to be true blockquotes (i.e., indented on left and right side). Resolved by restoring default margin to blockquote selector, and adding an override for blockquote.SVInsetFlow.