CSS doesn't apply when i change my Index.html 's directory

Hello? I'm using "startbootstrap-sb-admin-2-gh-pages".

There are some files including "index.html". And i wanna apply this bootstrap template to my existing code.

I wanna put Bootstrap's index.html into directory " /views ". (like /index.html ----> /views/index.html) But whenever I change this file's directory, CSS doesn't work.

I need to change some codes in css file. But i don't know how to change it.

Please give some advice. Thank you so much.

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When index.html was not in directory " /views " , sb-admin-2.min.css(css file) was applied.

but when i changed index.html's directory, it couldn't be found on f12(developers check).

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sb-admin-2.min.css code# (first part)

*/:root{--blue:#4e73df;--indigo:#6610f2;--purple:#6f42c1;--pink:#e83e8c;--red:#e74a3b;--orange:#fd7e14;--yellow:#f6c23e;--green:#1cc88a;--teal:#20c9a6;--cyan:#36b9cc;--white:#fff;--gray:#858796;--gray-dark:#5a5c69;--primary:#4e73df;--secondary:#858796;--success:#1cc88a;--info:#36b9cc;--warning:#f6c23e;--danger:#e74a3b;--light:#f8f9fc;--dark:#5a5c69;--breakpoint-xs:0;--breakpoint-sm:576px;--breakpoint-md:768px;--breakpoint-lg:992px;--breakpoint-xl:1200px;--font-family-sans-serif:"Nunito",-apple-system,BlinkMacSystemFont, .....................

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Css file is like this. So i don't know how to change if i want to apply this css to /views/index.html