Fix styling issues regarding the graphs and headers

Atlas currently has two general styling issues.

1. Incorrect indentation of the graphs on the relay and bridge pages. The graphs are too close to the left margin when compared to the general content above them.

2. Inconsistent use of the page-header class. The page-header class accentuate headers by adding a border underneath them. This class is used on the about page but the other pages manually add a horizontal rule to achieve the same effect.