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
You can use vh on the min-height property.
min-height: 100vh;
You can do as follows, depending on how you are using the margins...
min-height: calc(100vh - 10px) //Considering you're using some 10px margin top on an outside element