I sometimes come across websites where some clickable design element is floating on top of a scrollable element. This can be buttons, or banners or whatever. For me, they're always (always!) annoying.
Here's an example where the button covers other buttons. Granted, the area of the screen that is covered is very small, but still.
The button in this case opens a box which only ever contains some variation of "please upgrade your plan and pay us more money".
Is this just a dark design pattern to get users to do something, or is there a case where this is good practice? If there's text behind it, it might as well be a banner that covers the entire screen width, because I cannot read whatever is behind it anyway.