Not working with Flatsome theme

Hello,

I’m trying to add custom fonts styles in the text editor in my WordPress and I’m using Flatsome theme. Yet, it doesn’t work (I first tried with code and then with your plugin, none worked). It just does duplicate the “Formats” drop-down menu which is implemented in this theme. Is there any way to add a custom style under another menu ? For information, I’m still using the classic text editor.

See this screenshot : https://imgur.com/a/SYFEQ9m

Thank you.