Denied Editor Background

Mate,there is always nothing wrong with suggesting stuff,regardless of your position.
Now, what I get is that you would most likely want to change the dark theme,correct?

While it's true CSS is locked for you right now,it's an upgraded member feature,not a staff feature.You can customise it,if are Prime or above.

Also,there is a specific section dedicated to myBB ,themes etc.Feel free to take a look there.