Use of CSS

I’m new about vaadin. For a work project I’m developing a web server with Spring Boot and the web page with vaadin on Intellij. I have a file .css that contain all the selector for customize objects located in the folder ./frontend/themes/my-theme and when I run or debug project every style work. But when I package the project I don’t know (or I don’t understand) how can I “load” the css file to apply styles.
Can anyone help me?

Many thanks.

Does this help? Application Theme | Styling | Vaadin Docs

I’ve already follow those instructions to populate the folder frontend, in fact when I launch the program from Intellij the master stylesheet (styles.css) works. The problem arises when I package to production the project, the stylesheet doesn’t work, it seems like the program doesn’t find the customization files. There’s a way to tell to the program where it could find all stylesheet and images?

There shouldn’t be a difference between development mode and production mode. In other words, if the styles work in development mode, they should also work in production mode - you shouldn’t need to do anything extra. Either there’s a bug somewhere or you’re doing something in a strange way to cause the production build to lose the styles, but there’s not enough information to tell.

Maybe I did not say it clear enough. If I generate the .jar of my program and I launch from terminal (with java -jar) the stylesheet doesn’t work.

It should work. The reason why it doesn’t is not clear. It could be a bug or it could be something in your code. You could try taking a fresh project from and see if it happens there or not.