I'm not entirely sure if this is a bug, or if it's just me being an idiot. In my last game, I somehow disabled edge scrolling with the mouse, and a small red outline was around the edge of the screen for the remainder of the game. I could still drag the window via minimap, and I could also lock the screen on my champion and play that way. I wasn't able to fix it during the game, but when I entered a custom afterwards, everything was normal.
This may be an intended setting, so if it is, what's the hotkey to enable/disable it? otherwise, it's a bug so rito fix pls :P