Plone files modification

Hello all!
If I do a modification of a fragment file (like countdown2.css) directly in my website folder with notepad++ for example.
What should I do for this modification to be effective directly?

If you have copied the fragment to antother theme, the simplest way to do this is to remove the link in the and just use:

..... alll you css here .....

… or you could change the link in the fragment to wherever you decide to save the file

To be more precise:
I first tried to change the countdown2.css file directly with notepad++. It didn't work even after running bin/buildout.
So I toughts that this file had nothing to do with the website result and I leaved my first changes (like a background-color: red for example).
So I modified the css with a and it worked! My countdown was finally responsive (I used display:flex).
I Saved the files and I gave them to my school for my graduating thesis.
BUT: Now (two days after), I go back to my website and my surprise is that the first changes I made on notepad++ appeared and I have a background-color red....
Why do they appear so late ?

Sounds like browser caching.

I thought that too but even with CTRL SHIFT R it doesn't work and even if I try on another browser..

At least Chrome is hiding one level of refreshes from you. Second-click the refresh button with the dev tools open to get to the truest refresh option.