fix: Bug#5930 将主题设置为跟随系统后，再将鼠标移动到深色时，预览图的标题栏没有同步展示为深色

[DaiZW007]

修复悬浮预览主题，会受选中的主题影响

Log: 将主题设置为跟随系统后，再将鼠标移动到深色时，预览图的标题栏没有同步展示为深色

Bug: linuxdeepin/developer-center#5930

[github-actions]

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[DaiZW007]

I have read the CLA Document and I hereby sign the CLA.

[ArchieMeng]

+1

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This pull-request has been approved by: ArchieMeng, DaiZW007

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