Hey! 
The theme itself is “Better Light Than Never.” Entrants are welcome to interpret that as they see fit. As per the event page-
For this first event, Unreal Challenge: Better Light Than Never, we encourage you to create a short video showcasing your lighting abilities, pulling inspiration or guidance from the title itself. Build up a scene yourself, leverage available Marketplace products, KitBash3D’s provided content or anything else you’ve stashed away in your Vault, then make it shine! We want to see how you make those environments convey a feeling.
I hope this helps!