Set max-width and max-height to gif video (#13533)

app/javascript/styles/mastodon/components.scss

@@ -5575,6 +5575,13 @@ a.status-card.compact:hover {
   }
 }
 
+.gifv {
+  video {
+    max-width: 100vw;
+    max-height: 80vh;
+  }
+}
+
 .directory {
   &__list {
     width: 100%;