How can I can increase the font size for mobile only. I find that my <h1> are too small on mobile. The h1 is very large on desktop and too small on mobile.

I added the following to TheGem Child: Stylesheet (style.css):

@media (min-width: 480px) {

h1 {
    font-size: 8vw;
}

}

But nothing happened

Solved... I realized just now that I can view public tickets and I saw that this question was asked - and answered - before. So, I added custom css via Appearance -> Theme options -> General -> Advanced. It works. I'm as happy as an eskimo boy can be!

Here's my custom CSS that did the job:

@media (max-width: 500px) {
h1, .title-h1 {    line-height: 30px !important;    font-size: 30px !important;
}
p, .styled-subtitle {
 font-size: 20px !important;
}

With the "p, .styled-subtitle" code I increased the size of the main (body) text as well - only for mobile. Great!