You can still style links by opening the editor, going into the HTML, and then adding the class, styles, etc by writing directly in the code. You need to know basic HTML styling to accomplish this, but its almost identical to the knowledge needed to add styling using the old editor. The old editor was easier because it listed the option and you could put the code there, but it's not that different.
This functionality is now in the new editor. I highly recommend you switch to using the new editor, as the legacy editor will not be supported indefinitely.