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

#Header
{
width: 960px;
height: 150px;
}

#Content
{
min-height:100vh;
height: 100%;
width: 960px;
}