Modal Windows buttons hidden on mobile devices

Fixes for modal buttons on some iPhones to allow full screen and not have buttons hidden:
(Copy into the styles / CSS section of your app)

@media screen and (max-width: 600px){
.sweet-modal-overlay, {
    height: 100%;

It looks like this is the problem I have (testing on iPhone SE 2020).
Where would I put this code to make it work on my page? - Is there a usage example?

Copy the snippet above and paste into the sites CSS and you’re done.

Thank you. Still learning.
I hadn’t found where to edit the site CSS. I’ve found it now.
All good. Tested, and working as expected.