Improve README.md rendering with better CSS/style

Description

GitLab's rendering of README.md and other markdown files is not pleasant. It's annoying when I put a lot of work into a README.md and the content is not pleasant to read and looks untidy.

Right now the rendering of markdown is adequate, but it doesn't encourage people to read the content because it's not nicely laid out. It's important that README.md files are enticing.

Proposal

This is a highly subjective topic but I think some simple and concrete improvements that could be made are:

• Body font size should be increased, it's currently too small
• Width should be reduced by at least 25%. Paragraphs of text are currently too wide (contain too many words) which makes them harder to read when they span many lines. It's hard to scan visually from the end of one line to the start of the next when the page is too wide.
• Titles H1/2/3/4 should be better differentiated, their sizes are currently too similar

I am not a design professional (IANADP?) and I'm sure someone with that background could add a lot to the above suggestions.