Light grey bars along bottom of screen

Today I came back from a birthday party and began using my computer. After a couple of hours, I noticed that there's these light grey (translucent) bars along the bottom of my screen. They stay no matter what I do and I've tried restarting to no avail. They're only 1-2mm high and are very light - impossible to see on black backgrounds and only noticeable on white ones when looking at the bottom of the screen. I have attached photos of what it looks like when opening safari with internet off.

Edit: So I think this issue might be heat related. Before, when I was using a lot of things and it was hot, it looked like that. But now that it has cooled down, the bars are much lighter and even less noticeable. I have attached an image of what it looks like now (opening Safari WiFi off), running only Safari.