Add styling for Reddit video onebox.

diff --git a/app/assets/stylesheets/common/base/onebox.scss b/app/assets/stylesheets/common/base/onebox.scss
index 4c0a9f3..6d4f66d 100644
--- a/app/assets/stylesheets/common/base/onebox.scss
+++ b/app/assets/stylesheets/common/base/onebox.scss
@@ -188,7 +188,7 @@ aside.onebox {
 
       // full size images for instagram, twitter, etc.
       .aspect-image-full-size {
-        max-height: 500px;
+        max-height: 100%;
         width: calc(500px * var(--aspect-ratio));
         max-width: 100%;
 
@@ -280,6 +280,18 @@ aside.onebox {
       right: 10px;
       position: absolute;
     }
+
+    .reddit-video-icon {
+      &:before {
+        opacity: 0.8;
+        content: svg-uri(
+          '<svg xmlns="http://www.w3.org/2000/svg" width="32px" height="32px" viewBox="0 0 512 512" fill="white"><path d="M424.4 214.7L72.4 6.6C43.8-10.3 0 6.1 0 47.9V464c0 37.5 40.7 60.1 72.4 41.3l352-208c31.4-18.5 31.5-64.1 0-82.6z"></path></svg>'
+        );
+      }
+      bottom: 155px;
+      right: 50px;
+      position: absolute;
+    }
   }
 }
 
@@ -663,6 +675,13 @@ aside.onebox.stackexchange .onebox-body {
   }
 }
 
+.onebox.reddit {
+  div.description {
+    color: dark-light-choose($primary-medium, $secondary-medium);
+    padding-top: 10px;
+  }
+}
+
 .onebox.githubcommit {
   pre.message {
     padding: 0;

GitHub sha: 51217088