Banners: Read more carousel widget shows squares instead of 'pre' & 'next' icons

When clicking 'Read more' on the Essentials feature library page for the 'Banners' component, I see a carousel widget with two white squares. According to the DOM these should be glyphicons, but it seems that this icon-font is never loaded (probably needs to be our own hippo theme based SVG icons instead of glyphicons).