child theme styles in tinymce advanced editor

I have created a gradulicious pro child theme. I am using the TinyMCE advanced editor. How can I see my style customizations also in the editor? Without having to add my styles to two files: the child theme style.css and the tinymce editor-styles.css? I have tried by importing the styles.css into editor-styles using the @import css statement but this does not work. What is the best way to do this? Ronald