Launcher topbar should be always visible

Summary

The topbar notification background is transparent, when we scroll from the widget panel the topbar becomes not fully visible.

Steps to reproduce

Have some widget in order to be able to scroll, then scroll up from the widget panel.

What is the current behavior?

Widget content and topbar information are mixed.

What is the expected correct behavior?

Topbar is always visible.

Relevant screenshots

cc @rhandros @aude.m