Newsletter Sign-Up form using CSS flex and express.js

Hey everyone, so I did a little extra for this project😅. I thought, "The email shouldn't just end at console-logging, should it? 🤔". So, I decided to use express.js so that when the user inputs their email, it'll be sent to a server (my local server, in this case). As I learn how to use databases (like MongoDB) later on, I'll revisit this project so that I'll make the emails to be sent to and stored in a database, and maybe see how possible it'd be to send out automated emails🤷‍♂️.

Anyway, the issue I'm facing now is that after the success message has been closed, if the user is on a laptop and decides to minimize their browser window, all the elements become mashed up because the elements are now flex elements, and vice versa if the user is on a windowed screen and decides to maximize their browser tab because the section elements are now block elements. It turns out that the window.innerWidth and the window.screen.width properties aren't working as I expected them to🥲. I'd appreciate help on this🙏, and any comments about the rest of my solution as well.