You’ve effectively created a slide over sidebar. It’s an interesting hack to get there but IMO “should” properly be the domain of the browser.

See, I'm keeping my siidebar open most of the time, so I WANT it to cover the content that would otherwise be visible - said no one ever.

But yay, it's centered relative to the window now! God forbid the user tiles their windows, because it breaks the aesthetic the website author intended.

The internet has become so imbalanced in favor of what the website owner wants to run on my machine. I've still not found a reliable way of modifying user-hostile React pages. I'm sure before long it will take custom builds to avoid custom CSS being blocked by anti-tamper measures.