Reply To: Why does CSS negative margin left and right increase size of element?

[yeeyang]

Imagine, if you will, that margin in the wild generally tries to push things away from itself. A margin: 15px will push elements away by 15px. Now, imagine the inverse affect where margin is no longer push but pulling or stretching the element. So instead of pushing (15px) out from itself, now its pulling from itself (-15px).