Highlight color customization

[twistedmonkey]

I really appreciate your theme for thunderbird, I saw all the suggestion enhancement for the next version (if there will be one), so I thought to chime in and suggest another idea for customization that could be made through the addon option:

a custom hightlight color for the root.css right now the background color by default is:

--tree-background-color-selected: #3DAEE9;

but would be nice in windows 10 if it picks up the color accent the user set on the Windows color settings, like would do windows mail.

Or more simply just an option to set a custom color, so the final user can use the color he wants for selected items.

Just an idea. Anyway really dig the theme especially with the "more black" enahcmeneet for the toolbar.