Hi, I new to MAC and I say hi to all of you

Theres one thing I have notice on the screen.

At the bottom of the screen, left side as shown on the picture, theres a white line like its loosin color at the bottom.

I can notice this more in light colors then in dark colors.

I did not seem o notice this before till I had the IMAC on the backseat of the car for a long drive ,at a point it hit the back of my seat when I breaked hard on a red light.

Could this have done something or is it something else, is theres like a degausse or something?

heres the pic