Specifies the behavior of an element’s top margin if it is adjacent to an element with a margin. Elements can maintain their respective margins or share a single margin between them.
This property allows you to emulate the behavior of some browsers in quirks mode where table cell margins are collapsed into the borders of vertically adjacent cells.
-webkit-margin-top-collapse: collapse | discard | separate;
Two adjacent margins are collapsed into a single margin.
The element’s margin is discarded if it is adjacent to another element with a margin.
Two adjacent margins remain separate.