I like the 'Stylish' chrome extension. User created (or custom) styles for any website you use regularly. I use dark themes for practically everything.

My Hacker News style is a user stylesheet "Hacker News Dark" and 1 line of additional CSS I added to reduce the lane width of the text:

.comment-tree { max-width: 600px; }

Of course you can go to town and add comic sans, etc.