SingleDropDownList have hard encoded background color

[stephahn]

Affected Projects React

Is your feature request related to a problem? Please describe. When modifying background color using inner-class list of the SingleDropdownList. By default, list background color is defined as: <li id="downshift-1-item-0" class="" style="background-color: rgb(238, 238, 238);"><div><span>All categories</span></div></li>