Change message sidebar background?

.message { background-color: red; }

Yeah, but the message view is actually built with floats and they don't offer a sane way to have both the left and the right part to be of an equal height. The sidebar is usually much shorter than the message on the right, but by setting a background color for the message container it visually appears to be the same height. The content itself has a different background-color set, rounding up the illusion.

Take a look at the screenshot below, it shows how large the sidebar actually is compared to what it appears to be:

This is actually a quite common trick to counter this problem, luckily with the next major we can use CSS3's flexbox to create true equal height containers, eliminating the need for these kind of dirty work-arounds