Fix Main Page Diagram and Header

[gvanzin-allegheny]

The main purpose of this pull request is to fix 3 issues and improve the header on the site.

The three issues are as follows:

1. The diagrams on the main page are not transparent.
2. The diagrams on the main page are not centered.
3. The diagrams on the main page are not using the correct font as the other diagrams are.

This pull request fixes all 3 issues.

At the same time, it adds underlines to the topic lists in the header.

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