A button includes a keycap made of transparent material and including a first side surface and a second side surface opposite to the first side surface, a light guide block set on the first side surface of the keycap, and an ultraviolet lighting element set on the first side surface to emit ultraviolet light. Ultraviolet light emitted by the ultraviolet lighting element may enter into the light guide block, then is reflected by the light guide block to pass through the keycap to arrive to the second side surface of the keycap.