Stretching banner image to cover mobile screen

Site URL: https://corn-blue-m4pz.squarespace.com/

I'm using a code I found here to make the mobile header transparent. I have two problems I'd like to fix:

-Make the banner image stretch all the way to the top (logo size pushes the banner down after a certain size)

-Make the banner image stretch all the way to the bottom of the screen when you first open the website/page

I attached what it looks like right now

PW: squarespacehelp

Thanks!!