Hey there! This is code I made and I've noticed the issue too. It started happening with a recent Google Chrome update, as I haven't seen it happen on any other browsers, so I have no idea what changed to cause it. I recently found a fix for it, which involves changing an attribute in a parent div, but I'm not currently where I can get the code and instructions to you for that particular layout. I'll have it for you later on and I can either just put it here or you can add me on discord where I can help you one-on-one.

I was planning on putting the fix up on my CSS blog once I got all the affected base codes up, but you're right. If anyone happens by this before I can get to it, this'll be here (and yeah, Chrome updates in the background without notifying users, it's why this snuck up on me and confused the heck out of me until I worked with a friend to confirm that it was the reason behind the madness so to speak).

Here's the quick fix: In the CSS section there is a bit titled "SETTING UP" that's used as the base of the page. In that section is this snippet of code:

#wrapper #container #center {float:none; position:absolute; top:0px; margin:auto;}

All you need to do to fix the scrolling background is take out the position attribute (so take out position:absolute; and leave the rest). You could also change "absolute" to "relative" or "static" and you'll get the same effect.

However, that creates a new problem, and you'll have a bit of blank area at the bottom of the page (which is what the attribute was being used for) If that blank area is going to bother you, add the attribute below to fix it:

margin-bottom: -16px;

And you should be good unless Chrome decides to update and "fix" whatever it did. If you have any questions or are having trouble, let me know!