Are you on a mac? 99% of times it's because of an external mouse connected.

edit: the css for the element that overflows has: `grid-template-columns: 50vw 50vw;` and based on the spec: https://www.w3.org/TR/css3-values/#viewport-relative-lengths, scrollbars are not taken into account, therefore as long as you have a _forced_ scrollbar, the content WILL overflow regardless of your screen size.

By forced I mean a scrollbar you cannot remove and that's not enforced by your systems settings, you can clearly see this behaviour on mac if you toggle the "Show scroll bars" setting to "Always".

Safari and webkit based browsers can avoid this issues with `::-webkit-scrollbar{ display: none}` but it's not a cross browser solution nor a wise decision to hide scrollbars overall.