[DOC][UI]: Fix issues on light/dark theme

[yanCode]

This PR fixes: #3379
I used "next-themes": "^0.4.3", https://ui.shadcn.com/docs/dark-mode/next to handle the shifting of light/dark themes.

with next-themes, it can reduce much boilplate code to handle the changing of light/dark mode, and most importantly, it can easily get current theme, which will be used to control the theme of the code block prism-react-renderer

in which it uses github theme for the code block by using import lightTheme from 'prism-react-renderer/themes/github', when in light mode.

as an example:

also, after the fix. the scroll bar in dark mode looks better :

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