Does every div needs a set height? - html

Question

I'm stressing out because of a mindbreaker and I'm probably missing some essential, but easy thing.. And although I've done this many times before.. it's going wrong now.
So I'm creating a web app and always my starting point is
html, body {
height:100%;
width:100%;
}
And some of my inner elements have a set height in percentages and some in pixels.
However, to have some structure in my code, I'm setting up div's without a set height. Let's set up the following situation.
HTML
<div class="wrapper">
<div class="thisIsAStructureItem">
<div class="innerElement">
And just some untagged piece of text
</div>
</div>
</div>
CSS
.wrapper {
height:100%;
width:100%;
}
.thisIsAStructureItem {
/* nothing, not even height */
}
.innerElement {
height: 17.5%;
}
But in any editor or browser, because I haven't set a specific (%/px) height on the second element, it shows up as 0px, including all the inner elements.
So stupid as this might be.. What am I doing wrong?
UPDATE: See this JSFiddle
The situation makes it appear a set height is necessary, therefor so my title. Feel free to adjust to something more suitable
The situation above is a replica of a to-build-situation and using exact pixels is (at that above part) not an option. Please don't advice 'use X pixels'.

Answer 1

Original: http://jsfiddle.net/o0Lfyt0m
Updated: http://jsfiddle.net/o0Lfyt0m/1/ (from code sample below)
The innerElement is trying to display as 17.5% as tall as the parent element. The problem is that the parent element does not have a defined height. As a fall back to calculating 17.5% of undefined, the div's height is essentially defaulting to "auto" and assuming the height of it's content, which is based on the size of the font, line-height, padding etc.
Edit: A nice feature of CSS is that an elements styles can be inherited from it's parents. You can add a structure class which will inhert the height from it's parent element, which seems to be your intent.
You could even add this class to the body element, since it's height and width are identical to html... just not certain if the HTML element can be styled in all browsers, so I didn't do that.
html, body {
height: 100%;
width: 100%;
}
.wrapper {
height: 100%;
width: 100%;
}
.struct {
height: inherit;
width: inherit;
}
.innerElement {
height: 17.5%;
}
<div class="wrapper">
<div class="struct"> <!-- .struct inherits height/width from .wrapper -->
<div class="innerElement"> <!-- height calculated based on .wrapper -->
And just some untagged piece of text
</div>
</div>
</div>

Answer 2

Yes, you need to set the height 100% for that div too. Otherwise it's height is unknown and will not be able to take exactly the 100% height and innerElement height is not calculated accordingly.
To make sure, you must use the height 100% for that div too.
.wrapper {
height:100%;
width:100%;
}
.thisIsAStructureItem {
height: 100%;
}
.innerElement {
height: 17.5%;/* calc from it's parent div height i.e. thisIsAStructureItem*/
}
You are, in effect, asking the browser to calculate a height from an undefined value. Since that would equal a null-value, the result is that the browser does nothing.