How can an html element fill out 100% of the remaining screen height, using css only?

Question

I have a header element and a content element:

#header
#content

I want the header to be of fixed height and the content to fill up all the

Answer 1

You can also set the parent to display: inline. See http://codepen.io/tommymarshall/pen/cECyH

Be sure to also have the height of html and body set to 100%, too.