Opera 22.0.1471.70 (Windows 7 64-bit)
I've just installed Stylish to reduce the glare of some websites and noticed something when using the wikipedia-dark-light-width-clarity-by-splark style.
The black background has grey flecks that seem to be part of a repeated bitmap. These are not present when viewed with Firefox and are not related to the CSS. This is easily demonstrated by loading images from Wikipedia such as the ones below.
The downloaded images display properly otherwise, just the space around them is affected.