Div height:0px does not work?

Question

Setting a div height to 0px does not seem to work.

The div expands to show it

Answer 1

For me, on Windows 10, Firefox 58.0.1, it wouldn't hide completely unless using this:

display: block !important;
line-height: 0 !important;
height: 0 !important;
overflow: hidden !important;
zoom: 1 !important;
padding: 0 !important;
margin-bottom: 0;
border: none;