Federalism does not exist within states but between states and the federal government. Los Angeles (whether county or city) is an administrative subdivision of the State of California, not an separate sovereignty.
OTOH, Los Angeles isn't getting a .ca.gov domain because the state government doesn't want to dilute it's brand with local government websites, but that's about branding, not Federalism.
In my particular state, and in many but not all others, local governments whether that be counties, cities or towns are administrative districts which only have the rights and powers which the state chooses to delegate to them through state law and the particular charter granted by the state to the administrative district. The state through the normal legislative process can change those rights and powers or even eliminate a particular administrative district.