For the screen: brightnessctl s 0. But I think it’s a good idea to set this to a non-0-value before reboot in case the system saves this value.
For the LEDs: The newest keyboard firmware (from Git) has auto backlight dimming. But you can use the xLRGB command to set a black (000000) backlight color: Help running kbdgfx - #13 by pff