Fix html styling

[prisae]

Fixes the bad html styling for dark themes. The fix is done by simply removing all hard-coded colours, and leaving it up to the theme to decide on colours.

I tried a few of the Jupyter themes available:

I hope this would be OK with you @akaszynski (pinging you as you started with #82).

Closes #62

[codecov-commenter]

Codecov Report

Merging #88 (f76b387) into main (999d9ca) will increase coverage by 0.16%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #88      +/-   ##
==========================================
+ Coverage   87.15%   87.32%   +0.16%     
==========================================
  Files           4        4              
  Lines         366      363       -3     
==========================================
- Hits          319      317       -2     
+ Misses         47       46       -1     

[akaszynski]

This is probably the better solution.
@banesullivan, I’ll merge this if you’re fine with it.