add background property on playground canvas

[AmagiDDmxh]

Add background property to leva on the playground canvas style

ps: I don't know why is the package-name in pnpm lock-file got hashed, I believe is the newest feature of pnpm so I submitted it... If it doesn't make sense. plz tell me.

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Name	Status	Preview	Comments	Updated
cobe	✅ Ready (Inspect)	Visit Preview	💬 Add your feedback	Mar 18, 2023 at 5:23PM (UTC)

[shuding]

Thank you!