Boostrap.css of theme can't be changed, reloads old version after closing pinegrow [Answer provided]

I tried to modify (change the font import etc) in the “bootstrap.css” of the “bootstrap_themes” folder.
But after changing and closing pinegrow app, it reloads the old version of the css without the changes.
for me the workaround is: I can copy the boostrap.css and change the name into “boostrap_new.css” for ex., then it works. But it does notwork with the original file, why and is there a solution?
Thanks for information.

The CSS from the theme folder is automatically regenerated by Pinegrow when you activate the design panel and proceed to some changes. No changes should be done by hand on that particular file.

Instead, if you want to create specific rules, outside of the design panel, I advise you to create another CSS file.

Or when you use the Customize & update Bootstrap Theme (but in this case, the content of the theme folder is a bit different)

You should follow these instructions

Ah, ok. Thats what i finally did. Thanks you. Greetings