Hi there,
Thanks for writing in! Yes that is correct. CS preview is just for the preview. Because Cornerstone allows you to move things around, certain IDs, classes and selectors are not applied yet until actually viewing in the front end. CS only selectors are used in place so that you can move things around. For the most part what you do in the preview will show in the front end. There are just a number of these areas that need a little more checking if your customization requires it.
It’s best that you look at the actual page using something like chrome dev tools to see what the final selectors are so you can use that in the CSS.
Hope this helps clarify– thanks!