Force button to mobile navigation on desktop in 7.1

Site URL: https://gochristacademywf71.squarespace.com/

Using custom CSS I have forced my website header to display mobile navigation always.  However, the button is not wrapping into the mobile navigation on the desktop view.  Can anyone help me with the coding?  I've tried everything.  See the photo beneath.  I am trying to get that button to not display unless the plus sign is opened.

Your site is private. Can you setup password & share url again?