Fix docs templates of nesting, pagination, version header

Adds a new Documentation CSS file to correct the following:

- Subsections no longer indented (caused by nesting .section DIVs
  when sections created per subheading).

- Text in bullet points now black, not blue.

- Next/previous paging buttons now include spacing when page titles
  are too long and they sit on top of each other.

- Version header now aligned with nav menu on sidebar.

Closes #1542, closes #1583
[ci skip]