body, html {
	margin:	0;
	padding: 0;
	text-align: center;
}

ul#tabs{
	position: relative;
	list-style: none;
	margin: 0 auto;
	height: 27px;	
	width: 900px;
	background: rgb(170, 170, 170);
}
ul#tabs li{
	float: left;
	margin: 0 5px;
	height: 25px;
	text-align: center;
	position: relative;
	width: 150px;
	border: 1px solid transparent;
	top: 1px;
	background: rgb(128, 128, 128);
}
ul#tabs li:hover {
	border-bottom: 1px solid white;
	background: white;
}
ul#tabs a {
	display: block;
	height: 100%;
	text-decoration: none;
	color: white;
	font: 14px Arial, sans-serif;
}


body#course_info li#tab1,
body#announce li#tab2,
body#slide li#tab3,
body#hw li#tab4,
body#ta li#tab5 {
	background: white;
	border-bottom: 1px solid white;
}
ul#tabs a:hover,
body#course_info li#tab1 a,
body#announce li#tab2 a,
body#slide li#tab3 a,
body#hw li#tab4 a,
body#ta li#tab5 a {
	color: black;
}
ul#tabs span {
	display: block;
	padding: 4px 10px 0 10px;
}

iframe {
	position: relative;
	top: 0;
	bottom: 0;
	margin-left: auto;
	margin-right: auto;
	width: 900px;
	height:500px;
}