Needs to be in the sites main css file. Define color and positioning.

.cd-top {
	bottom: 20px;
	right: 20px;
	font-size:50px;
	color:#3ABE6B;
}
.no-touch .cd-top:hover, .no-touch .cd-top:focus {
	color:#3ABE6B;
}

http://codyhouse.co/gem/back-to-top/