Fix Version/s: None
This ticket is to improve the Rubin user guide theme based on some early user feedback:
- Reduce the contrast of table borders in dark mode to match the amount of contrast they have in light mode
- Increase the body front size. Currently it is 15 px; a more readable version would be around 17 to 18 px.
18 px worked out great, and we'll go with that.
In addition to improving tables in dark mode I also fixed a bug with the GitHub icon size in the nav bar.