Add a background colour to code elements

[inkyvoxel]

I love the Source theme, but I noticed that <code></code> and <pre><code></code></pre> elements have no background colour, which is common with other themes. My website has lots of code examples within posts, and using the Source theme makes them hard to read.

This is what code elements currently look like using Source:

This is what I would expect code elements to look similar to (please excuse shonky editing):