Gadget:oouiup.css

.backToTop {
	position: fixed;
	bottom: 20px;
	right: 20px;
}

.backToTop > .oo-ui-buttonElement-button {
	box-shadow: 0 1px 2px rgba( 0, 0, 0, 0.5 );
	border-radius: 50%;
	width: 48px;
	height: 48px;
	padding: 0;
}