Highlight "Actual Output" line in code output modal

[rabidbit]

Currently, when user is allowed to display output of their code, "Input", "Expected Output", and "Actual Output" use the same formatting. Per user study, would like to have "Actual Output" in view code output modal highlighted (to make it stand out compared to "Input" and "Expected Output"); this will minimize confusion on what the user should focus their attention on.

[seanlip]

Just a note that this issue (and #513) are a bit less straightforward than they might look on the surface. This is because they'll require forking the current MonospaceDisplayModal into two separate modals, one customized for code and the other customized for displaying output.