fix(module: back-top): fix visible styles

[ElderJames]

[中文版模板 / Chinese template]

🤔 This is a ...

• New feature
• Bug fix
• Site / documentation update
• Demo update
• Component style update
• Bundle size optimization
• Performance optimization
• Refactoring
• Code style optimization
• Test Case
• Branch merge
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🔗 Related issue link

💡 Background and solution

📝 Changelog

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🇺🇸 English
🇨🇳 Chinese

☑️ Self Check before Merge

⚠️ Please check all items below before review. ⚠️

• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
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[codecov-io]

Codecov Report

Merging #1005 (e832ab4) into master (471f5bf) will decrease coverage by 0.14%.
The diff coverage is 0.00%.

@@            Coverage Diff            @@
##           master   #1005      +/-   ##
=========================================
- Coverage    5.72%   5.57%   -0.15%     
=========================================
  Files         408     408              
  Lines       21834   21835       +1     
=========================================
- Hits         1250    1218      -32     
- Misses      20584   20617      +33     

Impacted Files	Coverage Δ
components/back-top/BackTop.razor	0.00% <0.00%> (ø)
components/back-top/BackTop.razor.cs	0.00% <0.00%> (ø)
components/tabs/Tabs.razor.cs	44.48% <0.00%> (-11.03%)	⬇️
components/core/Base/AntComponentBase.cs	37.17% <0.00%> (-5.13%)	⬇️
components/tabs/TabPane.razor.cs	90.47% <0.00%> (-1.59%)	⬇️

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