The cyan arm is connected to cyan gear that engages with pink rack-piston. At one end of the rack-piston is violet spring that accumulates energy during door opening and releases it during closing.
The spaces around the rack-piston contain oil. There are oil ways connecting the oil spaces including adjustment valves that regulate opening and closing speeds.
As the door swings closed, connecting link (in orange) comes into toogle with the cyan arm, giving it a large angular velocity, which helps the oil damping be more effective in retarding motion near the closed position.