html,
body {
	margin: 0;
	padding: 0;
	width: 100%;
	min-height: 100%;
}

body {
	background-image: url('blue_rock.gif');
	background-size: auto auto;
	background-position: center;
	background-repeat: repeat;
	padding-bottom: 80px;
}

body.bg-yellow {
	background-image: url('yellow_rock.gif');
}

body.bg-green {
	background-image: url('green_rock.gif');
}

.navbar {
	overflow: hidden;
	background-color: #333;
	position: fixed;
	top: 0;
	left: 0;
	width: 100%;
	z-index: 10;
}

.navbar a {
	float: left;
	display: block;
	color: #f2f2f2;
	text-align: center;
	padding: 14px 20px;
	text-decoration: none;
}

.navbar a:hover {
	background-color: #ddd;
	color: black;
}

.page {
	margin-top: 60px;
	padding-bottom: 80px;
}

.center-block {
	display: block;
	margin-left: auto;
	margin-right: auto;
}

.text-center {
	text-align: center;
}

.data-table {
	margin-left: auto;
	margin-right: auto;
	border-collapse: collapse;
}

.data-table th,
.data-table td {
	border: 2px solid #333;
	padding: 6px 10px;
}

footer {
	display: flex;
	justify-content: center;
	align-items: center;
	text-align: center;
	padding: 20px;
	background-color: #333;
	color: white;
	position: fixed;
	bottom: 0;
	left: 0;
	width: 100%;
	height: 60px;
	box-sizing: border-box;
}