Hey,
Little update: I searched the forum again and when using other keywords I managed to find the answer to my question:
Thread with the answer. And the relevant CSS classes:
.thumbnail-wrap:hover img, .thumbnail-wrap:hover video {
-webkit-filter: blur(20px);
-moz-filter: blur(20px);
-o-filter: blur(20px);
-ms-filter: blur(20px);
filter: blur(20px);
}
Thanks @mariusjopen for adding the code snippet in the other thread. I adjusted it to also work for video thumbnails.