system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why does it leave a mark when you press on your computer screen?
gpt
There is a very thin layer of liquid between the plates of glass/plastic that makes up the sandwich that is the LCD panel. An electrical charge twists the crystals in the is liquid so that they bend the light and allow it to pass through both the front a rear polarize layers. 

The amount of twist depends on the strength of the electric field and the thickness of the liquid crystal layer. That's why the color changes when you push on it. The messed up color stays around for a bit because it takes some time for the liquid crystal to flow back. Pressing hard enough can damage the damage the area and make it permanent.