When using the Tab key to cycle through the elements on the page, you should be able to press either Space or Enter/Return to activate whatever element currently has focus. If you open the Control Center (by tabbing to its toggle button and pressing Space or Enter/Return), you can further tab over the elements. The problem is, some of these elements can't be activated. The four buttons that don't seem to work are the three buttons under the Theme section, and the button in the top right to close the Control Center. I'm unsure why the three buttons under Theme don't work, but the close button in the top right isn't even a button element, so it's not surprising why that one doesn't work.
I'm using Firefox on macOS, but I can test other browsers too if needed.
When pressing Space or Enter/Return when an element currently has focus, it should have the same behavior as if it were clicked.
