In version 1.3, I made some changes to the sidebar so that it will work a bit more reliably than it did previously. As part of that, the semi-transparent background was actually taken from the sidebar and added to the body via a ::before in the CSS. But because of that, the changes you had made to remove the animation won’t affect it. I think that’s getting you here.
Let’s do this first.
Go to your theme options page and choose the Advanced tab.