CSS Layout Debugger
A tweet-sized debugger for visualizing your CSS layouts. Outlines every DOM element on your page a random (valid) CSS hex color.
One-line version to paste in your DevTools
$$ if your browser aliases it:
~ 108 byte version
If you prefer to watch video tutorials with live-coding, then check out this series I recorded with the same contents as in this article: Egghead.io - Introduction to Reactive Programming.