.add-to-calendar a.external {
padding-left: 20px;
background-size: 16px 16px;
background-repeat: no-repeat;
background-position: left center;
}
.add-to-calendar a.google { background-image: url(https://upload.wikimedia.org/wikipedia/commons/a/a5/Google_Calendar_icon_%282020%29.svg); }
.add-to-calendar a.outlook { background-image: url(https://upload.wikimedia.org/wikipedia/commons/8/8c/Microsoft_Office_Outlook_%282018–present%29.svg); }
.add-to-calendar a.yahoo { background-image: url(https://upload.wikimedia.org/wikipedia/commons/2/24/Yahoo_Calendar_icon.svg); }
.add-to-calendar a.ical { background-image: url(https://upload.wikimedia.org/wikipedia/commons/d/d4/Icon-Calendar.svg); }