I can't tell if CHVRCHES is pop or electro. It seems like some songs would be for the radio, but some songs by them are more for dancing and I can't decide on what exact genre they are.
This answer to another question states - and I would agree - that it's possible for a song or band to be 'pop' and belong to another more specific genre at the same time. As to that more specific label, I don't think 'electro' is necessarily a good fit for Chvrches as it refers specifically to a style of electronic funk originating in the early 80's. (It's also used to describe acts who work in other styles, but not in a way that seems to have found broad agreement). 'Electronic', on the other hand, is a much more general term that would be appropriate.
Although it's another broad genre, synth-pop seems perfect for Chvrches if you need a single label.