I need to add 20px of margin on mobile sitewide, but adding the @media query didn’t help b/c there looks to be another piece of code over-riding it. I was able to get it to work when inspecting the element and adding padding: 0 20px manually (underlined in red in picture below), but I don’t know where to find this. Most forums about the subject are from 2016 or so.
Here is what I added to my custom CSS tab, which didn’t work:
@media (max-width:480px){
.x-main.full {
padding: 0 20px;
}
}

Here is the original @media query, which you can see is missing the padding element and also has the width set to 782. So where is this code so I can change it to 480 and add 20px padding?
