It doesn’t really matter if they accept it or not, you’re doing it on your own time. The US may be different, but here you employeer have zero say in what you do in your spare time. Don’t use company issued equipment or software licenses, that changes thing, and may count as misuse of company property and that can get you fired.

Most companies I’ve worked for have a provision that states they can buy my projects, by compensating me for my work.