Instructor from Wiltshire Ron Groves did a video & traffic light routine with us years ago
Careless was essentially a green, sticks foot out trips opponent close in slow pace (free kick sufficient) maybe a word in his delicate shell-like on the way past
reckless, not in control, not bothered about opponent's safety, included tripping opponent who's running at great speed (was free kick & yellow card)
and dangerous say deliberate use of elbow, foot over the ball, above the knee, used disproportionate force or excessive force as it later became (warranted a free and a red card)
Think Ron's on the Isle-of-Wight nowadays, smashing bloke, great instructor.