Today I stumbled over an interesting blog post by Gajus Kuizinas which was linked in the very interesting newsletter of Webdesigner News. The idea is to inject a CSS style snippet into a web page to show the layout of all web page elements. This can be achieved by setting a different translucent background color for every depth of nodes. This way you can see the size, the margin and the padding of each element on the page and can easily spot errors while developing the layout of a web page.
For every nesting level, a different translucent background color is applied.