Hi! I'm glad that you like my solution. Unfortunately, there is no extension, I do it with CSS only.
You need to get discussion ID (for instance, ID of this discussion is 30117) and use in the code below:
li[data-id="id-of-thetopic"] .DiscussionListItem {
background-image: linear-gradient(to right, #fff, rgba(255,255,255,0)),URL(your-url.com/your-image.jpg) !important;
background-repeat: no-repeat;
background-size: initial;
background-attachment: scroll;
background-position: center top;
}
