Custom stylesheets

Hi all,
I come back to this subject to tell of a misadventure.
Note: I use Joplin to prepare a newsletter via email, then I copy/paste the formatted page in my message.

Here is the problem
1- if the external style sheet is imported, I lose the formatting
2- if the styles are included in the Joplin note, the formatting is kept

To troubleshoot, I exported the note in html, then I copied the content of the web page.
Is there a better way to get around this or should I continue to include my styles in the note?

Edit: I’ve found a possible roundabout, importing my stylesheet by this syntax
@import url("absolute path to stylesheet.css") than by the simple string syntax.
Thanks to w3school!

Could you confirm if I’m right or not?