Is this border+background intended? !ScyphTlOY6 No.13403
Thumbnails in #mature threads now have a border around them, and a background that appears in transparent images. That Lyra picture is supposed to be just Lyra on top of transparency, nothing else.
I don't think there's any reason to make them look different from non-#mature threads...
But anyway, since I suspect this is an accidental change that happened because of the new Spoiler and NSFW images, allow me to take the opportunity to say that I really like the new ones.