How to make a pure css triangle which has a white center

Question

I want to create an upward and downward facing arrow with css like the following: http://apps.eky.hk/css-triangle-generator/

However, instead of a solid color, I want to

Answer 1

I think you could get a good idea of what to do by checking out this tutorial on pure css thought bubbles. It's doing what you're looking for.

http://www.sitepoint.com/pure-css3-speech-bubbles/