Put a background on the tooltip.

This was provided by default in waybar but since I had to wipe out existing CSS to work around display issues in the latest release, I've had to add the background color to the tooltip back in manually.

ansible/roles/waybar/files/style.css

@@ -52,6 +52,10 @@
     font-size: 10px;
 }
 
+tooltip {
+    background-color: #323232;
+}
+
 /* Each module */
 #battery,
 #clock,