Mobile Menu Color cannot be changed.

Hi there,
Menu background color works fine in desktop, but not on mobile/tablet mode.
I used theme customize and change the colors for both mobile and tablet mode, but it won't have any effect, still showing the default white.

Any kind help will be greatly appreciated, thanks
PS: I have already gone through the mobile option in the theme customise, it has no effect after i saved it.

 

Thanks for the help,
after I disable the static CSS file generation, nothing happen and it doesn't work.

here's the link: https://ncar.mgwales.uk/

Thank you very much for your help.