To apply, send some of your previous works. If we like your style, you will be cast. It is important to have a unique style.

Most scenes will happen during the night, in the city, though there will be a lot of moments where they will be on their base which looks like a modern sleek-looking white room. 

It's much better if you draw them yourself. If you make backgrounds from free resources online, it's fine if you do a good job and guarantee that there won't be any copyright problems in the future.