DropDownList Colors for the List That Displays

How do you change the background and text colors of the List that displays once you click on a DropDownList? I have searched all of the code for the color that is currently displaying which is #1E90FF, and can't find it anywhere. I assumed that you would be able to modify the .ListItemRenderer something like this, but it did not work:

.ListItemRenderer {
background-color: #2B8D00 !important;
color: #323233 !important;
}

Start by locating the DropDownList entry point and its ListItemRenderer styling, then inspect how the opened list receives the current #1E90FF background and text colors. Verify whether the requested CSS customization is supported; done means the displayed list can use the requested background and text colors without relying on an ineffective .ListItemRenderer rule.

Written by the indexing model from the issue text.