whe to put css file?

Hello, i am new i Vaadin.
I am building web app usin Maven project. I have read book.
After I add webapp directory in to src/main. After building project thems folders were created automaticaly.
I tryed to use @Theme("runo"). Automaticaly was created folder src/main/webapp/VAADIN/themes/runo, but it is empty.
I need to customise it add my theme. src/main/webapp/VAADIN/themes/mytheme. Then I create file styles.css and
add next strings to it.

@import "../runo/runo.css"; .beagleTheme { @include runo; /* An actual theme rule */ .v-button { color: blue; } }
But it dosn't work. As it seems to me it could not find runo.css.
I tryed the same with valo. The same result.
What am I doing wrong?