Background-color of `pre` and `code` blocks is horrible

The background colour of `pre` and `code` blocks is `#8effe0` which looks horrible for highlighting code.

We could do with adjusting this to some better background colour with rouge syntax highlighting enabled.

## Information

Code background colour is set in `_scss/_01_settings_colors.scss`. In #168 `background-color` has been disabled for both `pre` and `code blocks to attempt to solve.