width and height

[EXCUSE]

...
<div style="width:0px">
<input type='text' ><br>
<input type='text' ><br>
</div>
...

...
<div style="height:0px">
<input type='text' ><br>
<input type='text' ><br>
</div>
...

2 above are the same except the attribute of <Div/>: one is 'width' and other 'height'.
Somebuddy pls tell me why with 'height' the <Div/> collapses itself and hides components inside, while the attribute 'width' doesn't?
I mean, actually with 'width', the <Div/> still collapes but components inside isnt Hidden.
Components the whole except the Iframe.

Pls tell me the reason.
Im noob and
Thanks in advance.

[Snookerman]

They should both look the same.