fix(filmstrip-only): override Atlaskit background for transparency

css/_base.scss

@@ -28,6 +28,16 @@ body {
     }
 }
 
+/**
+ * AtlasKitThemeProvider sets a background color on an app-wrapping div, thereby
+ * preventing transparency in filmstrip-only mode. The selector chosen to
+ * override this behavior is specific to where the AtlasKitThemeProvider might
+ * be placed within the app hierarchy.
+ */
+.filmstrip-only #react > .ckAJgx {
+    background: transparent;
+}
+
 p {
     margin: 0;
 }