I love the feature of black background with green text on Wiki!
How it works
First, go to the "Appearance" tag and switch to the "Monobook" skin (by switching to the Monobook radio button and hitting the Save button at the very bottom). Then go to the Gadgets tab and, at the bottom of the "Appearance" section in that tab, check the box for "Use a black background with green text on the Monobook skin" and hit the Save button at the bottom again.
It usually works well. However, starting from yesterday, anomaly happened since the left side of screen was no longer black, and the grey icon of Wikipedia was shifted from very left side to top-middle area so that it blocked part of the main text on the top. Any solution for this? Thank you!