Improve exercise card design

[flacial]

Problem

In the /exercises/js0 or any other lesson slug, the exercise cards code highlighting looks off in which any mathematical operators have a white background, and the code itself has its own background.

Expected look

without the extra space under the question and the white background of the minus operator

why? it looks less cluttered because the question has been moved outside and the code has its own area between the problem text and the question.

Actual look