Fixes#121. Additional, fixes include:
* Light tables, title/hr underlines, code and quote blocks on the
dark theme
* Scrollbar not rendering on top of content
Cleanup includes:
* Removal of css rules that are internal to github (eg. octicon)
* Merging of duplicate or overridden declarations
* De-duplicating light and dark theme using import + custom properties
Improvements include:
* Using Fira / Fira Mono for rendering (as is done in the text editor)
* Using relative units as much as possible, making it much easier to
use a responsive design in the future
* Using the same background color for a more seamless experience
* Adjusting color contrast for the background changes, ensuring proper
accessibility while still using GitHub's style
Gonçalo Silva