Stop quarrelling, as actors do backstage (6)

I believe the answer is:

makeup

I'm a little stuck... Click here to teach me more about this clue!

'stop quarrelling as actors' is the definition.
I can't judge whether this definition defines the answer.

'do backstage' is the wordplay.
'do' becomes 'make' (synonyms).
'backstage' becomes 'up' (I can't justify this - if you can you should give a lot more credence to this answer).
'make'+'up'='MAKEUP'

Can you help me to learn more?

I've seen this clue in The Irish Independent.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.