Darkdown.css is an adaptation of Kevin Burke's beautiful Markdown.css which offers much better default styling for your markdown files.
Darkdown.css is an adaptation of Markdown.css primarily altering the background and text colors, with a few other minor changes.
See an example of this style in action here.
Add the following to the top of your markdown files:
<link href="http://github.com/yrgoldteeth/darkdowncss/raw/master/darkdown.css" rel="stylesheet"></link>