Windows 7's "color hot-track" effect for the web

Anyone remember Windows 7's much-hyped "color hot track" effect that would show for active entries in the taskbar?

I always thought it looked cool, so I set out to deconstruct the effect by drawing a lookalike in Illustrator. I realized that it was simple enough that it could be implemented with a combination of CSS and some (simple) Javascript. I decided to deploy this effect on on the latest version of my portfolio!

Wondering how it works, or want to use it in your own website? The entire portfolio is open-source, so check it out on Github!