Styling WebListBox scrollbar colors?

Is there a simple way to change the default color of the WebListBox ‘thumb’?

On my Firefox browsers (desktop & mobile) the thumb is a dull blue color (I’m not sure where that color choice comes from as it doesn’t look like the scrollbar color used elsewhere in the browser.) The default color sticks out like a sore ‘thumb’ against color palette used in my application.

Can’t find a way to do it within Xojo.

You could create a personal.css file and change the colors for the thumb and load the file using the App HTMLHeader.