Div block banner disappearing behind Nav bar, but not in designer

Hi guys,

So after a lot of trial and error mixed with many an online tutorial, I’ve almost completed my website project.

I’m running into an issue with mobile view that i thought had been solved when looking at the designer - but when looking at the site on an actual phone, that is not the case.

As you can see in the below screenshot, the banner is 1/2 hidden behind the Nav bar:

But when i look at it in designer, it appears to be fine:

Here is my site Read-Only: Read Only Link