$dropdownmenu-background is not used

[rlhawk]

What should happen?

A color defined in the $dropdownmenu-background variable should cause a dropdown menu to have that background color.

What happens instead?

The defined color is ignored.

Possible Solution

The $dropdownmenu-background variable should be used in a CSS declaration in the foundation-dropdown-menu mixin.

Test Case and/or Steps to Reproduce

How to reproduce:

1. Define a color to $foundation-dropdown-menu.
2. Create a dropdown menu.
3. Observe that the defined color is not used for the background color of the dropdown menu.

Context

This issue affects the ability to set a background color for a dropdown menu through Foundation settings.

Your Environment

• Foundation version(s) used: 6.5.0-rc.1
• Browser(s) name and version(s): Firefox 61.0
• Operating System and version (desktop or mobile): macOS 10.13.5

Checklist (all required):

• I have read and follow the CONTRIBUTING.md document.
• There are no other issues similar to this one.
• The issue title is descriptive.
• The template is correctly filled.