style: fix BackTop not hidden completely

[jesse3mh9a]

[中文版模板 / Chinese template]

🤔 This is a ...

• New feature
• Bug fix
• Site / documentation update
• Demo update
• Component style update
• TypeScript definition update
• Bundle size optimization
• Perfermance optimization
• Refactoring
• Code style optimization
• Test Case
• Branch merge
• Other (about what?)

🔗 Related issue link

💡 Background and solution

📝 Changelog

Language	Changelog
🇺🇸 English	Fix Backtop still interactive when it is hidden.
🇨🇳 Chinese	修复 Backtop 隐藏时仍然影响布局, 尤其是容易触发光标样式

☑️ 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
• TypeScript definition is updated/provided or not needed
• Changelog is provided or not needed

[ant-design-bot]

[ant-design-bot]

[afc163]

Try

.ant-back-top:empty {
  display: none;
}

[jesse3mh9a]

Try

.ant-back-top:empty {
  display: none;
}

嗯 用:empty伪类 会更好 我修改下

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[jesse3mh9a]

@afc163 谢谢你的建议, 已经修改完成

[fireairforce]

🤔这个lint挂的好奇怪。。