But if I place this code into style.css instead, it doesn't work. Interestingly, styling the other form elements from style.css this way works just fine. Only the Submit button has issues.
I don't want to use the Layouts CSS because it loads too late and for a while the Submit button can be seen with its default design before my custom CSS is applied.
What can be the problem? How can I style the button from style.css?