Check out example codes for "hwo to reload css in flask". It will help you in understanding the concepts better.

Code Example 1

if facing no changes quickly then do this content point.....

Is it possible that your CSS is being cached by your browser? – ...
yes , if i manually reload the server the output is being changed ! – ...
Try Hard Refresh - Ctrl + F5 or hold Ctrl and click on the Refresh button on your web browser. –

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