Floating element with 100% height

Question

I have a element (represented as aside) that I need to span the full height of the page. However, the height is appearing to be ineffective with "height 100%".

Here is the fiddle: http://jsfiddle.net/h18ctmfq/

aside{
        width:300px;
        float:left;
        background-color:#808080;
        height:100%;
    }

Answer 1

Add this

html {
    height: 100%;
}

JSiddle Demo