<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
<style>
html,
body {
height: 100%;
width: 100%;
margin: 0;
}
#fixed-height {
height: 100px;
background-color: #ebcaca;
}
#remaining-height {
background-color: #ebe6e6;
height: calc(100% - 100px);
}
</style>
</head>
<body>
<div id="fixed-height">
Fixed height
</div>
<div id="remaining-height">
Remaining height
</div>
</body>
</html>