What does 'height: 0;' mean in CSS?

Question

I am working with some old code of css. At many places they have declared height as height: 0;. what this 0 means and in which unit it is?

Can anyone help me out.

Answer 1

in css height means the physical height of an element.

it is same as height:0px or height:0%.

suppose the following html elements one is having a property height:0; and another is having a property height:100px let's see what happen

#me {
  height: 0;
  background-color: #333;
}
#me2 {
  height: 100px;
  background-color: #333;
  color: white;
}

<div id="me" style="">this is an element</div>
<br/>
<div id="me2" style="">this is an element</div>

Answer 2

"0" doesn't need an unit as height:0; is the same as height: 0px; or height: 0%;

height:0;

The result really depends on what element is targeted: EX:

#parentdiv{height:0;}

This just maked the parent div is 0px in height, but that doesn't mean that the child div will not show up, that will only happen if overflow:hidden; would be used also. So it really depends on what element it was appended to.