Screen test
Clean the screen, turn the brightness up, then go through the colors full screen. Click, tap or press → for the next one, ← to go back and Esc to leave.
Found a stuck pixel? Some come back after gently massaging the spot through a soft cloth with the screen off. Dead pixels (always black) can’t be fixed at home.
Your screen
Browsers see the screen in CSS pixels; physical pixels are those times the pixel ratio. The refresh rate can read low on battery saver or when the tab is in the background.