doc: change select color

[JinIgarashi]

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Description

Please describe what you changed briefly.

Type of Pull Request

• Adding a feature
• Fixing a bug
• Maintaining documents
• Others ()

Verify the followings

• Code is up-to-date with the main branch
• No lint errors after pnpm lint
• Make sure all the exsiting features working well

Refer to CONTRIBUTING.MD for more details.

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Latest commit: 551e45b

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