Removing scrollbar shifts page to the right

Hi guys I have a quick question about disabling scroll.

If you scroll down on my homepage and click the hamburger menu, I want to disable scroll which I have achieved by making the body have a combo class of overflow hidden, and toggling it with custom code.

Although it works, in Chrome the browser’s scrollbar gets removed, causing the whole page to snap to the right every time. I’ve tried to counter this by adding margin to the body-overflow-hidden-class, but it still snaps. The menu which slides down is position fixed, maybe this is the issue?

Thanks in advance!

Live site here:
Read-only here: