Thank you very much for the reply.
That is a step in the right direction. Now the primary menu stays active as the window shrinks.
However, it now stays active for all sizes, even the smallest devices.
Could it be because this custom CSS comes at the very end? Perhaps the original CSS which handles the responsiveness to window size has to be in a specific order?
If there’s any logic I can add here at the end, to keep the mobile-friendly menus below a specified size, please let me know.