Where to start with a CSS media feature proposal

Hi, I've been a web developer and open source contributor for a long time,
but I'm honestly still a bit unaware of W3C's processes. Is there a
proposal system similar to ECMA TC39 where I can sponsor a proposal without
joining or paying member fees? I have an idea that I think will be an
important privacy and security improvement, and while I can make a
proprietary implementation, I want it to be standardized to gain more
traction.