If you're customizing your theme and the visual editor isn't displaying changes in real time, it's usually due to your SSL certificate.

Try this first:

1) Go to "Settings" on the left side of your Wordpress, then click "General".
2) Change your "Wordpress Address (URL)" and "Site Address (URL) to make sure it has "https://" instead of "http://" and click "save changes".

If that doesn't work, it's an issue with how the SSL certificate was installed at your host. Make sure to secure ALL URLs. For WPEngine users, it looks like this: