Responsive landing page using flexbox

Hi! This is my solution for the Huddle landing page. I've used Javascript to validate the email and give a custom 'error' message upon an invalid input. I did struggle with the validation pop-up that seemed to already be present. It seemed to be a browser thing and the only way I could disable it was by putting 'novalidate' on my form. Would love to hear if anyone has any tips for this.

Would also love some general feedback! ^^