docs(action-sheet): update css vars

[liweijie0812]

🤔 这个 PR 的性质是？

• 日常 bug 修复
• 新特性提交
• 文档改进
• 演示代码改进
• 组件样式/交互改进
• CI/CD 改进
• 重构
• 代码风格优化
• 测试用例
• 分支合并
• 其他

🔗 相关 Issue

💡 需求背景和解决方案

• feat(ActionSheet): item attribute enhancement #845
  css vars 文档更新补充

📝 更新日志

• fix(组件名称): 处理问题或特性描述 ...

• 本条 PR 不需要纳入 Changelog

☑️ 请求合并前的自查清单

⚠️ 请自检并全部勾选全部选项。⚠️

• 文档已补充或无须补充
• 代码演示已提供或无须提供
• TypeScript 定义已补充或无须补充
• Changelog 已提供或无须提供

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.67%. Comparing base (02b774b) to head (a9922e6).
⚠️ Report is 359 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff              @@
##           develop     #847       +/-   ##
============================================
+ Coverage     6.93%   56.67%   +49.74%     
============================================
  Files          400      287      -113     
  Lines         4241     7305     +3064     
  Branches       990     1983      +993     
============================================
+ Hits           294     4140     +3846     
+ Misses        3947     3165      -782     

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[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/tdesign-mobile-react@847

commit: b96dc48

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