<div id="wrap">
	<div id="head">
		<span>head</span>
	</div>
	<div id="body">
		<span>body</span>
	</div>
	<div id="foot">
		<span>foot</span>
	</div>
</div>

html,
body {
	padding: 0;
	margin: 0;
	background-color: #fff;
	font-family: monospace;
	font-size: 18px;
	line-height: 1.4;
	color: #fff;
}

* {
	box-sizing: border-box;
}

#wrap {
	display: flex;
	flex-direction: column;
	min-height: 100vh;
}

#head, #foot {
	flex: 0 0 auto;
	height: 100px;
	background-color: #000;
	padding: 10px;
}

#body {
	flex: 1 1 100%;
	background-color: #777;
	padding: 10px;
}