Hm, that page did not come up for me; if that is a page-editing screen, only you can access that, so we'd need to see the actual published page that's live on your site. Also, note that testing cart buttons in your page-editing screen may not work right, but should work fine when the page is published to your live site.
I tested the cart buttons on all 4 of your training-guides sales pages and found the cart looked and worked fine there. Note that since the overlay-style cart is a fixed size, if a buyer adds 5 different items or more to their cart, that would make the cart larger than the overlay window can contain, so in that case a scrollbar would appear.