fix(site): demo style bug in dark mode

[thinkasany]

[中文版模板 / Chinese template]

💡 Background and solution

问题来自于这边，dark模式的时候也显示了这个白色
https://github.com/ant-design/ant-design-web3/pull/1031/files#diff-af695945508383dfe144f45e21777064d77a86b72855098465b575d5c832f4b4R8

🔗 Related issue link

close #1120

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Name	Status	Preview	Comments	Updated (UTC)
ant-design-web3	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Aug 29, 2024 2:56am

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