Newsletter forum alignment on mobile vs. desktop

I want my newsletter form to be aligned left on desktop and centered on mobile.  I have tried several codes, but nothing seems to work. I have used custom CSS to make this newsletter form and I believe it is preventing the code i've tried from solving this issue. 

Any help with this would be greatly appreciated, as this is the last thing I have to complete before I can publish the website. 

https://www.gildedageantiques.com/

ps: Williamsworld

@Macey You can add this code under Website > Pages > Website Tools > Custom CSS

.newsletter-block .newsletter-form-body {
    display: flex;
    justify-content: center;
    gap: 5px;
}

If you want to center the newsletter form only in the footer, use this code instead:"

#footer-sections .newsletter-block .newsletter-form-body {
    display: flex;
    justify-content: center;
    gap: 5px;
}