[Glitch] Add blurhash

Port front-end changes from fba96c808d to glitch-soc

Signed-off-by: Thibaut Girka <thib@sitedethib.com>

app/javascript/flavours/glitch/styles/components/media.scss

@@ -117,6 +117,8 @@
   text-decoration: none;
   color: $secondary-text-color;
   line-height: 0;
+  position: relative;
+  z-index: 1;
 
   &,
   img {
@@ -131,6 +133,21 @@
   }
 }
 
+.media-gallery__preview {
+  width: 100%;
+  height: 100%;
+  object-fit: cover;
+  position: absolute;
+  top: 0;
+  left: 0;
+  z-index: 0;
+  background: $base-overlay-background;
+
+  &--hidden {
+    display: none;
+  }
+}
+
 .media-gallery__gifv {
   height: 100%;
   overflow: hidden;