What caught my attention was a nice combination of LibreOffice UI and menu customization. LibreOffice allows documents to carry the customized user interface menus, toolbars and much more. If you have a document that requires a specific set of commands you can customize the user interface in Tools - Customize and store the user interface in your document. When opening the document in another machine with LibreOffice, the user interface carried by the document is displayed. I used this feature professionally when I had to convert some old Excel macros to LibreOffice and the macros had hundreds of lines just to modify the user interface. I drop these lines, did the changes in UI once and stored in the document.
So I applied the same strategy to the Styles menu. I was glad to see that you can format your document with little amount click or by activating the style menu with the keyboard. All my custom style were in the menu.
Then closed my document and opened a new document. I wanted to apply my custom styles as before but hey... it does not work. The custom styles were just doing nothing.
The trick is to customize the Styles menu with your preferred styles and add them to your document instead of the LibreOffice Writer interface (the default). This detail slipped under my nose.
Lessons learned: If you want a document with custom styles in the Styles menu, create a template with your custom styles and custom user interface and each new document based on the template will have everything set up.
Happy Text Styling !