i see a small red shadowed line in only the black screen

i bought a used DELL LATITUDE 7490 , the screen appears normal in normal colors , but when i access to a black screen i see a small red shadowed line in only the black  screen ,if you ask where ,in the bottom a little to the center , exactlly in the position of the frame up to the mouse if you close the monitor , so i want to know if this is due to the bombed frame , or something dangerous that  need to replace the screen ,thqnks for responding.