>1 pixel tall underline on paper-dropdown-menu-light shows both active and inactive underlines when active

[bmwalters]

Description

If the underline on a paper-dropdown-menu-light is greater than 2px (styled using the --paper-dropdown-menu-input mixin as recommended by the file), and you make the dropdown active by clicking on it, you can see both the active underline and the inactive underline.

Expected outcome

You should only see the active underline when you focus the dropdown.

Actual outcome

You can see one pixel of the inactive underline as well as the active underline.

Live Demo

https://jsbin.com/suwesodegu/edit?html,output

Steps to reproduce

1. Place a paper-dropdown-menu-light on the page.
2. Style it as seen in the JSBin live demo.
3. Focus it.
4. You will see both underlines.

Browsers Affected

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