Fix Panel overflow

Summary: Panels need to let their content overflow, for example the color picker.

Reviewed By: priteshrnandgaonkar

Differential Revision: D21404621

fbshipit-source-id: 70498e335c9fcb3767aaef2bbd2ce22324adc8e5

desktop/app/src/ui/components/Panel.tsx

@@ -121,7 +121,7 @@ export default class Panel extends React.Component<
       borderTop: 'none',
       flexGrow: 1,
       padding: props.padded ? 10 : 0,
-      overflow: 'hidden',
+      overflow: 'visible',
     }),
   );
   state = {