make current section clearer

[tehlowkeywiz]

It is currently hard to know in which section you are (EOSIO, Ethereum, Platform) from a quick look at your screen. For a better UX, I believe the bg color of the top banner should be different, depending on the section that you're currently in.

e.g. using the brand color as the bg color of the section's top banner
EOSIO: #111A44
Ethereum: #8B93B3
dfuse Platform: #FF4660

@avionrouge feel free to make suggestions to enhance the UX as well.