twitter/bootstrap — pull request #2940 by grantzau (2012-04-04 10:17:30+00:00)
Title: +Support for transparent colors in gradients "horizontal" and "vertical"

These gradients do not work, when one of the colors are "transparent". To make it work:

The background-color needs to be transparent.
The IE filter doesnt support "transparent" as a value, so "#00000000" is used instead.

I have made three conditional versions of the two gradient to do this. To aviod repeating the background-image part, which is the same for all three, I made two helpers.