int Alpha = 75; // sätt ett tal mellan 1-100 (%)

LONG Beta = GetWindowLong( Handle, GWL_EXSTYLE );
SetWindowLong( Handle, GWL_EXSTYLE, Beta | WS_EX_LAYERED );
SetLayeredWindowAttributes( Handle, 0, ( 255 * Alpha ) / 100, LWA_ALPHA );