fix layout beautiful when browser changes size !

[zhuzhuyule]

PR Checklist

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• Tests for the changes have been added (for bug fixes / features).
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PR Type

What kind of change does this PR introduce?

• Bugfix.
• Code style update (formatting, local variables).
• Feature.
• Refactoring (no functional changes, no api changes).
• Build related changes.
• CI related changes.
• Documentation content changes.

What is the new behavior?

Description about this pull, in several words...

• Screens with this changes: you can resize brower, when brower size between 767px and $content-desktop(or $content-desktop-large) , the layout is terrible and the sidebar not hide.

• Link to demo site with this changes: zhuzhuyule.com