When you add an item to the cart it changes the header from full width and only having a blue menu bar to being a box completely blue. It fixes the problem when you remove the item from the cart.
Images to how what I mean
without items - https://i.sstatic.net/93hhQ.png with items - https://i.sstatic.net/OAvyI.jpg
the link to the site is image-displays.com