Template:UltimateGuitar/styles.css

.mw-ui-button::before {
	background: url(https://upload.wikimedia.org/wikipedia/commons/thumb/b/bf/Ultimate-Guitar.com_logo.png/30px-Ultimate-Guitar.com_logo.png);
	content: '';
	display: inline-block;
	height: 30px;
	margin-right: 6px;
	width: 30px;
	vertical-align: -10px;
}