I inspected your html and found the problem.
Don’t know how you managed it but you had a session tag in your page HEAD tag, like:
<dmx-session-manager id="session1"></dmx-session-manager>
because such tag is not allowed in the head - it essentially breaks the whole html so the editor couldn’t find the rest of the tags and that is why visual editing was actually pretty much disabled.
So move this tag into the body, refresh then everything and then the editing should work fine.