position: absolute, , top bottom, div:
<!DOCTYPE html>
<html>
<head>
<style>
body { height: 100%; margin: 0; }
#felso { height: 100px; }
#also { position: absolute; top: 102px; bottom: 0; left: 0; right: 0; }
</style>
</head>
<body>
<div id="felso"></div>
<div id="also"></div>
</body>
</html>
. 102px top - , 1px * 2 #felso.
jsFiddle Demo