Relative sizes for mail notification
HTML mail notification templates don't use any fixed sizes (px), only relative ones (em). That implies that each mail client sets the parent sizes.
The problem is with mail clients that have an "uncomfortable" parent font size. For example the main diff area, which has
font-size: 1em; translates to 10px size in Gmail. At that size it is hard to read.
Maybe we need to set to the main block a parent font-size of some fixed value in order to reset mail client defaults. For instance 13px seems to be optimal absolute size for mail contents.