html {
	height: 100%;
}

body {
	height: inherit;
	display: flex;
	flex-direction: column;
	justify-content: space-evenly;
	align-items: center;
	font-family: 'Tahoma';
	font-size: 40px;
}

.box {
	flex: 0 0 auto;
	box-sizing: border-box;
	width: 100px;
	height: 100px;
	text-align: center;
	border-top: 1px solid #687291;
}

.box:nth-child(odd) {
	background-color: #dfe1e7;
}

.box:nth-child(even) {
	background-color: #eeeff2;
}

#F {
	background-color: #687291;
	border: 4px solid black;
	display: flex;
	justify-content: center;
	align-items: center;
}