[WIP] Fix 'Copy Markdown' button functionality in docs

[Copilot]

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This section details on the original issue you should resolve

<issue_title>[bug] "Copy Markdown" button doesn't work</issue_title>
<issue_description>in docs page like: https://www.casbin.org/docs/biba, "Copy Markdown" button doesn't work, it shows error:

Failed to copy the markdown to your clipboard. Please copy it manually.

need to fix</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [bug] "Copy Markdown" button doesn't work #55

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