Why Does Height: 100% on a Child Element Not Apply When the Parent Element Has a Min-Height/Max-Height Value But No Height Value

Why does height: 100% on a child element not apply when the parent element has a min-height/max-height value but no height value?

In the first case, you don't have any height defined so it's clear that the precentage height on child will fail.

From the specification:

Specifies a percentage height. The percentage is calculated with respect to the height of the generated box's containing block. If the height of the containing block is not specified explicitly (i.e., it depends on content height), and this element is not absolutely positioned, the value computes to 'auto'.

min-height is only a boundary and the height of your element still depend on its content. If you will have one that exceed 300px the element will have more than 300px

.container {
  background-color: red;
  width: 500px;
  min-height: 300px;
  padding:10px;
}

.child {
  background-color: blue;
  width: 500px;
  height: 400px;
  animation:change 2s linear infinite alternate;
}
@keyframes change{
   from {
     height:100px;
   }
}

<div class="container">
  <div class="child">
    
  </div>
</div>

percentage height to child inside of parent element with view port height does not work

There are two issues preventing your code from doing what you want:

Class names cannot contain certain characters, like percent signs and as user 3in0 mentioned - square brackets which can be confused with the CSS attribute selector.
Percentage heights are based on the parent's height, but not it's min/max height, which are not factored into the calculation. I assume you are using min-height given the classname, so your 90% child height will be 90% of auto (inital/default value). Auto essentially means 'whatever height you need' - 90% of auto = auto.

.min-h-80vh {
  background-color: seagreen;
  height: 80vh;
}

.h-90 {
  background-color: coral;
  height: 90%;
}

<div class="min-h-80vh">
  <div class="h-90">test</div>
</div>

Why inner div is not taking 100% of parent div?

Its a bug when parent height is determined by min-height/max-height children with percentage heights are sized incorrectly.

Just use some other method to assign the height, may be fixed or by using flex or whatever. In following example I added display:flex; to parent and flex: 1; to child:

.full {
  background: yellow;
  display: flex;
  height: 100%;
  width: 100%;
  position: absolute;
  justify-content: center;
  align-items: center;
}

.outer {
  background: blue;
  min-height: 100px;
  min-width: 300px;
  display: flex;
  flex-direction:column;
}

.inner {
  background: red;
  height: 100%;
  width: 100%;
  flex:1;
}

<div class="full">
  <div class="outer">
    <div class="inner"></div>
  </div>
</div>

Child with max-height: 100% overflows parent

When you specify a percentage for max-height on a child, it is a percentage of the parent's actual height, not the parent's max-height, oddly enough. The same applies to max-width.

So, when you don't specify an explicit height on the parent, then there's no base height for the child's max-height to be calculated from, so max-height computes to none, allowing the child to be as tall as possible. The only other constraint acting on the child now is the max-width of its parent, and since the image itself is taller than it is wide, it overflows the container's height downwards, in order to maintain its aspect ratio while still being as large as possible overall.

When you do specify an explicit height for the parent, then the child knows it has to be at most 100% of that explicit height. That allows it to be constrained to the parent's height (while still maintaining its aspect ratio).

Child inside parent with min-height: 100% not inheriting height

This is a reported webkit (chrome/safari) bug, children of parents with min-height can't inherit the height property: https://bugs.webkit.org/show_bug.cgi?id=26559

Apparently Firefox is affected too (can't test in IE at the moment)

Possible workaround:

add position:relative to #containment
add position:absolute to #containment-shadow-left

The bug doesn't show when the inner element has absolute positioning.

See http://jsfiddle.net/xrebB/

Edit on April 10, 2014

Since I'm currently working on a project for which I really need parent containers with min-height, and child elements inheriting the height of the container, I did some more research.

First: I'm not so sure anymore whether the current browser behaviour really is a bug. CSS2.1 specs say:

The percentage is calculated with respect to the height of the
generated box's containing block. If the height of the containing
block is not specified explicitly (i.e., it depends on content
height), and this element is not absolutely positioned, the value
computes to 'auto'.

If I put a min-height on my container, I'm not explicitly specifying its height - so my element should get an auto height. And that's exactly what Webkit - and all other browsers - do.

Second, the workaround I found:

If I set my container element to display:table with height:inherit it acts exactly the same way as if I'd give it a min-height of 100%. And - more importantly - if I set the child element to display:table-cell it will perfectly inherit the height of the container element - whether it's 100% or more.

Full CSS:

html, body {
  height: 100%;
  margin: 0;
}

#container {
  background: green;
  display: table;
  height: inherit;
  width: 100%;
}

#content {
  background: red;
  display: table-cell;
}

The markup:

<div id="container">
  <div id="content">
      <p>content</p>
  </div>
</div>

See http://jsfiddle.net/xrebB/54/.

Why Does Height: 100% on a Child Element Not Apply When the Parent Element Has a Min-Height/Max-Height Value But No Height Value