Source code color should be darker (legibility) (BB-3638)

Looking at a page of code I wrote, I can barely read it even though I'm using a new monitor in a well-lighted room.

See for yourself:

• https://bitbucket.org/mlissner/search-and-awareness-platform-courtlistener/src/62087a438c30/alert/lib/mojibake.py

The code that's in a comment is light gray, a lot of it is light orange, and even the code itself (at the bottom of the page) is really hard to read.

Would really appreciate not having to squint to read my own code.