title: HTML/CSS: Create a div that always fills the entire page... and then a resizeable div within it?
body: <p>I feel like this is an easy question, but for whatever reason I can't figure it out today. </p>
  
  <p>I need a div that always fills the entire page, no matter how large that page is. Then I need another div which I can re-size with javascript (mydiv.style.width = x; mydiv.style.height = y;). </p>
  
  <p>If the second div is resized to be taller than the existing browser window height, the first div should resize to fit. </p>
  
  <p>i.e. If the first div's background color is red, I should <em>never</em> see any white background color, because the first div always expands to the size of the entire page. </p>
  
  <p>I tried this, it doesn't work because the red background doesn't expand to the size of the entire page:</p>
  
  <p><a href="http://www.academickeys.com/tmp/test.html" rel="nofollow noreferrer">example of the problem</a></p>