Answer: Great question, come with long answer 🙂
Keyboard backlight is thin plastic layer that is black color and covers in between the keyboard and the logic board area, look at the link below that shows the keyboard assembly and you can see the keyboard backlight plastic layer in the 3rd picture.
After all if your lucky sometime tiny drop of liquid can get trap in a not so sensitive area of the laptop and maybe just make your keyboard a bit sticky but most of the time that is not the case,
smallest amount of liquid damage sometimes take a long time to show and cause trouble to the components such a logic board or flex cables or even make the Li-ion battery Swelling and best option is to open and clean the liquid damage area as soon as possible before corrosion damage occurs,
Clean up the area using new toothbrush and 95% to 99% isotope alcohol that can be found at pharmacy stores before actual damage and than need to put everything back together and that is not so easy and you should consider the risk ion your doing that your self,
Safest way to save your laptop and data is also the most expansive option, Make sure not to use the laptop and do not attempt to turn it on, air dry the excessive liquid if needed and do not put in rice bag as that case additional damage due to the rice dust,
If you can disconnect the battery until liquid damage is cleaned or the bad part is replaced, do not turn on and take it to experienced technician,.
Hope that was helpful, Good luck 🙂