Arrow appearing on icons

I can’t link to the page because the site’s not up yet, but I’ve installed Simple Social icons on a couple of sites without an issue.

I’ve just added them into a footer widget on a new site and they are overlaid by an arrow – like a “play” button – which makes them pretty ugly. The arrow colours also change on hover but there is no obvious place to change the hover colours as they’re different from the ones I’ve already specified.

I’m not great at CSS but I’ve searched for anything that might be causing this via the inspector but I can see nothing. This bug seems to have arrived since the latest WP upgrade, but that might be pure coincidence.