Matt Gemmell released a script to help author's unobtrusively mark what they felt to be their main points. Not one person said, "can't this be done in pure HTML & CSS?", yet I slapped together a solution anyway.
I've embedded an example below, or if you're into Codepen (like the cool kids), then head over there and do me one better.
Check out this Pen!
Update (2013-05-17): I corrected a spelling error. Mr. Gemmell’s features two m’s which I failed to notice earlier.