cstytcss4.css

.yt-core-image--fill-parent-width {
    width: 100%;
    filter: blur(15px);
}
.yt-core-image--fill-parent-width:hover {
    width: 100%;
    filter: blur(0px);
}


.yt-core-image--fill-parent-height:hover {
    width: 100%;
    filter: blur(0px);
}

.ytp-cued-thumbnail-overlay-image:hover {
    filter: blur(0px);
}

.yt-core-image:hover {
 filter: blur(0px);
}
.
.yt-core-image--loaded:hover {
 filter: blur(0px);
}
ytd-thumbnail:hover {
    filter:blur(0px);
}