Polymer/core-menu-button — pull request #6 by Sing-Li (2014-08-06 21:44:20+00:00)
Title: gray demo background to surface any overlay painting problems

There is a long standing bug with both Firefox and Safari where the overlay is missing the background. Similar to a fixed problem with the paper-menu-button:

https://github.com/Polymer/paper-menu-button/issues/4

Changing the body to gray on demo will surface these kind of problems earlier.