Wiktionary
bright as a button
a. 1 (context simile English) Very bright (clever, smart, or crafty) 2 (context simile English) Very cheery, energetic and upbeat.
Usage examples of "bright as a button".
If he did not know his lessons, he always had some droll excuse to offer, and as he was usually clever at his books, and as bright as a button in composing answers when he did not know them, he got on pretty well at school.
When God was a schoolboy, it occurred to him in the heavenly play ground, along with young Satan, his school friend, who was as bright as a button, to create the world.