CSS strange when scrolling horizontally, resize issue

Hi there, I have strange issue,
my site:

https://www.gmdventures.com

When I resize the window for my website, and then I scroll horizontally, the header and the footer are not expanding and there is a break in the css. I’ve tried looking around, setting width to 100% but nothing.

So to recreate the error load the website and then shrink the window until a horizontal scroll bar appears.