Casey's custom css for Markdown-Here http://markdown-here.com/
Go to the settings page for the markdown-here Chrome Extension.
In the field "primary styling", paste-append the contents of the file default.css in this repo.
Markdown-here periodically updates their css to be more cross-browser compatible and standard. I put my overrides at the bottom of their default styling, but there may be conflicts - double-check it looks how you'd like before sending :)
If something looks funny, try their default first and then try these additions one at a time.
This css is primarily targeted at gmail users (like the students at Yale university). The rounded-borders headers that look so sleek don't work in every email client.