nextcloud/plugins/audioplayer/style.css

#audioframe{
	position:absolute;
	top:0px;
	left:0px;
	height:100%;
	width:100%;
	background:rgb(20,20,20);
	background:rgba(20,20,20,0.9);
	text-align:center;
	display:table;
}

#audioframe>div{
	display:table-cell;
	vertical-align:middle;
}

#audioframe>div>div{
	display:inline-block;
}