table.thirds{
	width:100%;
	border-collapse:collapse;
	border:1px solid #999;
	background:#ffc;
}
.thirds tr{
	vertical-align:top;
}
.thirds th{
	text-align:left;
	background:#9f9;
	width:33%;
	border:1px solid #999;
}
.thirds td{
	width:33%;
	border:1px solid #999;
}
.center{
	text-align:center;
}
.bg {
	background:url(backhtml.gif);
}
.exercises .bg{
	background:url(Buttback.gif);
	border:1px solid #333;
	text-align:center;
	padding:.25em .5em;
}
.exercises{
	float:right;
}
.code{
	background:#ffc;
}