KWK - your image doesn't render for me, but I did have a look through the page code and I can see that Mark's using Font Awesome to provide the icons (see https://fontawesome.cc/Files/). As far as I can see from a brief look it's consistent across the site; for instance a folder icon is created by:
<i class="far fa-folder fa-lg"></i>
in both the listing and search results. The apparent switch to the white on black rather than black on white (now styled back to blue) would have been down to using the fas rather than far class by intent or typo, I think the code was actually generated as this in fact:
<i class="fa fa-folder fa-lg"></i>
Just my 2 Ningis worth...