Responsive coming soon landing page made with CSS flexbox

I initially used relative/absolute positioning to achieve the overlay effect of the submit button but ended up changing the margin instead as the overlay wasn't uniform across all screen sizes. I am not sure about the box-shadow effect seen on the button in the design specifications. I wanted to add a hover state for the submit button but ended up scrapping the idea. I did not add a script.js for form validation since the required parameter seen on the email input field achieves the same effect.