Styling using custom properties broken in v2.0.0

[jkczyz]

Description

Styling a paper-dropdown-menu with custom properties no longer works in v2.0.0.

Expected outcome

Custom styles are applied to the paper-input-container.

Actual outcome

Custom styles are not applied to the paper-input-container.

Live Demo

https://www.webcomponents.org/element/PolymerElements/paper-dropdown-menu/v2.0.0/demo/demo/index.html

Compared to a working demo with v1.5.1.

https://www.webcomponents.org/element/PolymerElements/paper-dropdown-menu/v1.5.1/demo/demo/index.html

Steps to reproduce

Look at the last demo at:

https://www.webcomponents.org/element/PolymerElements/paper-dropdown-menu/v2.0.0/demo/demo/index.html

Browsers Affected

• [X] Chrome
• [ ] Firefox
• [ ] Safari 9
• [ ] Safari 8
• [ ] Safari 7
• [ ] Edge
• [ ] IE 11
• [ ] IE 10