How does Coinbase Exchange calculate trading fees?

As a cryptocurrency enthusiast, I'm always interested in understanding the fees involved in trading. Specifically, with regards to Coinbase Exchange, I'm curious about how they calculate their trading fees. Do they have a flat rate for all transactions? Or is it based on the amount being traded? Additionally, do they charge higher fees for certain types of transactions, like margin trading? Understanding these details would help me make more informed decisions when trading on the platform. I'd appreciate any clarity you could provide on Coinbase Exchange's trading fee calculation method.