Nueva Template - Increase Poster Text Size on Mobile Cover Page

How do I make the poster text bigger on the mobile version of my homepage? The template is Nueva.

Screenshots attached for reference. There is a second section below this one where I'd like to achieve the same look.

Site: https://grouse-apricot-2ba7.squarespace.com/

Thank you in advance!

@rebeccaosullivan add to Home > Design > Custom CSS

@media screen and (max-width:640px) {
div#block-d82e42d81aac5e81e70e h1 {
    font-size: 500px;
}
}