Whenever you create or edit a new page with the Categories, Products, Pages, or Store Editor apps, you'll see a preview window on the right that displays the page in real time as you build it. This is the Storefront Panel.
The Storefront Panel has a consistent options menu regardless of the app you're in:
You can collapse the window by pressing x. To re-expand it, press the desktop monitor icon:
To expand the window so that it overlays the Editor Panel on the left, press the divider icon:
Press it again to revert the division to its default setting.
By default, the Storefront Panel is set to half the width of your monitor display. To change its width to fit a specific device type, press the device icon and select the width of your choice:
You can use the device selector to set the window to desktop width, tablet width, mobile width (smartphone), or full screen. You can also click the left side of the window and drag it to any custom width you prefer.
To take a shortcut to the Store Editor app, press the pencil icon:
To open the page in a new browser tab and see the full storefront experience, press the icon next to the URL: