Did the air pressure in the cabin increase or decrease after the plane took off?

Common sense: the higher the altitude, the lower the air pressure, and the more difficult it is for human beings to breathe ...! Early airplanes, because the cabin was not sealed, after the plane took off (with the increase of flying height, the air pressure also decreased) ...! Modern aircraft is a sealed cabin. After take-off, the air pressure in the cabin increases with the flight altitude (manual adjustment).