making mobile nav styling uniform

Site URL: https://therare.la

password: rarity

Hello,

i'm having some trouble styling the mobile navigation menu so that 

a) it looks the same on all devices

b) each menu item is evenly spaced (both main and subnavigation on mobile)

As you can see, when i shift to the subnavigation, the top two boxes change in dimension and don't look uniform with the others. Additionally, the menu hides some items depending on what device it's viewed on. Even in the squarespace emulator, it looks different when one enters full screen preview mode.

Thank you for the assistance!