I accidentally created nearly the same effect here, go to the knowledge base and click recent changes to see it from live page. The only thing that has a gradient fill is the background for the links.
What we're looking at is the background color for the toolbox which is one solid color. Go left to right where space is between rss and atom, it looks like it gets darker on the right side but it's one color left to right.
If you look where it says toolbox left to right as you can see it's the same color.