Step 1 - To save work in progress, simply click this icon to exit full screen or just press the Escape button on your keyboard.
Step 2 - From here you can now see the save button and click it.
Step 3 - To preview the page outside of the Editor, simply click 'copy link' on the tab you are currently working on. This will also prompt a notification stating the Link has already been copied.
Step 4 - Paste the link on a new tab from your browser. And you can now see the page you created.