PLEASE HELP! Second Domain within my site isn't mobile friendly

I created a sales landing page for a new project on my site, www.thinkwiththings.com. I added code to hide the header and footer and did web forwarding to connect it to a new domain name. www.thingslab.app.  It looks great under my original domain name on mobile, but when using the web-forwarded domain, the mobile version shows the desktop version. (so all text is unreadable) This is the page under my site https://www.thinkwiththings.com/thingslab-app this is how it looks in the new domain  https://www.thingslab.app/ on desktop both are fine, only mobile is bad. I added this additional code:

<script type="text/javascript">

if (screen.width <= 767) {document.location = "https://www.thinkwiththings.com/thingslab-app";}

</script>

But then nothing shows up at all on mobile?!?!?!?

The code I have in the Page Header Injection works great to hide the header and footer, but like I said when I add the other it all disappears. I have tried only to add the above and it still shows nothing:

<style>

  #header { display:none }

</style>

<style>

  .header, #footer-sections{

    display:none !important; }

</style>

This is on my phone. Looks fine

@tuanphan Thanks for the response. Yes that is the desktop version, so text isn't readable. The mobile version on Squarespace looks like this. So, all text is readable. I don't understand why it works when looking at the page under my 1st domain, but in the new forwarded domain it only shows up as desktop version. Can you help as it all launches tomorrow and I really don't want to use the first domain name, but might have to as I can't solve this. 

Thanks, Jules