Why is this on my screen? What even is it??

So I have a windows 9 PC and this (Picture in comments) just appeared in my browser (opera GX) when I got on today. It appears on multiple websistes such as reddit and speedrun.com. It always appears at the top of the tab and goes away when I scroll down. I don't know what it means so I have no clue how to fix it. I've tried restarting my PC but that didn't work. I don't know what else to do.