private void tema()
{
    var registro = My.Computer.Registry.GetValue(@"HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Themes\Personalize", "AppsUseLightTheme", null);
    if (registro == 1)
        Interaction.MsgBox("Tema claro");
    else
        Interaction.MsgBox("Tema oscuro");
    return null;
}