Margins will never collapse for a box with an overflow value other than visible.
Value
auto The behavior of auto isn??™t specified in any detail in the CSS2.1
specification. In existing implementations it provides scrollbar(s) when
necessary, but it doesn??™t show scrollbars unless the content overflows
the element??™s box.
hidden hidden causes content that overflows the element??™s box to be clipped.
No scrolling mechanism will be provided, so the overflow will be
invisible and inaccessible.
scroll scroll clips overflowing content, just like hidden, but provides a
scrolling mechanism so that the overflow can be accessed. This scrolling
mechanism is present whether the content overflows the element??™s box
or not, to prevent it from appearing and disappearing in a dynamic
layout. When the output medium is print, this value allows overflowing
content to be printed (as if the value were visible).
visible visible allows overflowing content to be visible. It will be rendered
outside the element??™s box, and may thus overlap other content.
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