Hi @karenjoslin, sorry you are having preview troubles.
At Appearance > Custom Design > CSS, or through Appearance > Customize > CSS, you should be able to preview your CSS changes in that page in real-time with no need to click a button. Are you not seeing the CSS changes appear in the preview as you add your CSS?
One suggestion would be to log out, clear your browser cache and cookies, restart your browser and then try again.
I hope that helps, and please let us know if you are still not getting the real-time preview when adding your custom CSS.