public record MyTheme : LumexTheme
{
    public MyTheme()
    {
        DefaultTheme = ThemeType.Light;

        Light = new ThemeConfigLight()
        {
            Layout = new LayoutConfig() { /* ... */ },
            Colors = new ThemeColorsLight() { /* ... */ },
        };

        Dark = new ThemeConfigDark()
        {
            Layout = new LayoutConfig() { /* ... */ },
            Colors = new ThemeColorsDark() { /* ... */ },
        };
    }
}