You also have the ability to display your custom font styles in the admin panel by adding them to the /assets/css/admin.css file. This will help the backend to match the fonts on the front end as closely as possible.
You can find the file in the FTP under www > css > admin.css.
Just add the styles being used on your front-end site to the admin.css file. After clearing your browser's cache, the font styles can be seen in the Content Editor.
In order to make the additional styles available in the Styles menu within the Content Editor, you will need to edit the /admin/styles.js file. Note: Pay special attention to the js syntax in order to make sure that it will work properly.