Cursor doesn't line up correctly on some examples

[nfischer]

If you click on the fibonacci example (lets say, on the last line), the cursor won't be adjusted quite right. It'll look as if it's partially between lines 14 and 15 (mostly on 15, where it should be). Once you start typing, everything works looks correct once again.

This has to do with adding in the underlines, which increase the height of the lines. This is something that ideally should get fixed, since it's annoying for examples with lots of underlines.

Or, we can investigate different styles, like tinting the background with a lighter shade of a lighter color, instead of underlining.