在高度和宽度为100％的div内以％设置div的高度

Question

I have the current html structure

<release_cover> 
    <overlay_controllers>  Green Div </overlay_controllers>
    <img src="blu.div" />
</release_cover>

And I want to achieve this:

The img tag is the blue container. The magenta is the release_cover tag.

I have problem in setting the overlay_controller tag (the green) at a 20% height, exactly positioned at 80% of the container.

So far i did:

release_cover{
  width: 100%;
  height: 100%;
  position: relative; 
} 

release_cover img{
  width: 100%;
  height: 100%;
}

overlay_controllers{
  min-height: 20%;
  margin-top: 80%;
  position: absolute;
  width: 100%;
}

Unfortunately the height of the green div depends on what's inside and not a fixed 20%.

Suggestions?

(example with the suggestions received so far: https://jsfiddle.net/82Lb0nhe/ )

Answer 1

You could position overlay_controllers using top instead of margin-top property:

release_cover {
    width: 100%;
    height: 100%;
    position: relative;
    display: block;
}
release_cover img {
    width: 100%;
    height: 100%;
}
overlay_controllers {
    position: absolute;
    top: 80%;
    height: 20%;
    width: 100%;
    overflow: hidden;
}

Answer 2

Using a combination of absolute position along with top , while also not allowing a height greater than 300px it will compute correctly:

.container {
    width: 300px;
    height: 300px;
}
overlay_controllers {
    z-index: 2;
    bottom: 0%;
    position: absolute;
    margin-top:;
    height: 20%;
    width: 100%;
    background-color: #fc0;
}
release_cover {
    top: 0px;
    width: 100%;
    position: relative;
    display: block;
    overflow: hidden;
    margin: 0px;
    padding: 0px;
    max-height: 300px;
}
release_cover img {
    padding: 0;
    margin: 0px;
    z-index: 1;
    width: 100%;
    height: 100%;
}

Working fiddle: https://jsfiddle.net/fL98w9of/