Post layout problem

Can you set it to 2000px with my CSS above applied so I can see?

Also disable or turn off your caching plugin.

I currently don't see the CSS being applied and the container width is still 1200px.

Sure one moment please

Okay. I have done what you requested. Can you check now?

Looks like it's working:
https://www.screencast.com/t/tmmaXGchMlz

But the space still very big on right side. Is there a way to decrease this space: https://imgur.com/a/nkwzEl9

That's the sidebar. You can either remove it if you aren't using it:
https://docs.generatepress.com/article/sidebar-layout/

Or make it narrower:
https://docs.generatepress.com/article/sidebar-widths/

Ok. Thank you very much

No problem :)