What browsers are you supporting and testing against, both for the editor and its output? For example, the text widget doesn't allow spaces to be typed on Firefox, which makes me wonder about the compatibility of the generated code.

Edit: Also, kudos for having such easy, frictionless access to the demo. I also really like the structural parity between the desktop and mobile versions.

Edit2: How are you picking which version (desktop/mobile) to show? Are you doing some kind of sniffing, rather than relying on media queries? I'm not getting the version I expect when I change the viewport's size in my DevTools: Chrome always gives me the mobile version in responsive mode, while Firefox always gives me the desktop layout unless I spoof a device's user agent string...