Named CSS color variables defined with wildcard scope in one CSS file are not visible when imported by another CSS file. Example:

Theme.css:

* {
    theme-backgroundDark: #335588;
}

Main.css:

@import url( "/styles/Theme.css" );

#messageListPane {
    -fx-background-color: theme-backgroundDark;
}

Result:

WARNING: Could not resolve 'theme-backgroundDark' while resolving lookups for '-fx-background-color' from rule '*#messageListPane ' in stylesheet file:/C:/xxxx/styles/Main.css