Be careful of what chemical you use because some will dissolve plastic or weaken it. 90% pure isopropyl alcohol is safe, but don't use anything oily, like WD-40. Don't put the keyboard in the dishwasher because water and detergent can stay trapped under silicone rubber key cups or clear flexible membrane circuit boards.

Hold the keyboard long side up over a sink or some paper towels, with the keys slightly forward of vertical, and spray alcohol into it, starting at the top and working down. Keep doing that until the liquid comes out clear. Let the keyboard dry in that position or with the keys facing down for several hours in a warm room or in a car parked in the sun with the windows rolled up almost all the way.