Bug 34875: offsetLeft broken within CSS3 columns

There should not be any red spans visible.

This test checks that offsetLeft and offsetTop return correct values when used on elements contained in multiple columns. We put a number of red spans (of arbitrary size) in a multi-column div. The script at the end creates an identically sized green span for each of the red spans, and places it at the offsetLeft and offsetTop of the red span, using absolute position. This ensures that the green span completely covers the red span.