Hello! I'm trying to edit the text styles on mobile, but I can't seem to get the media queries to work? Can anyone provide any help here?

Here's the site: http://www.kate-leisy.com/

It's H1 wrapped in a span, so I've tried H1, ._H1, ._H1 span, etc. Here's the css below...

@media only screen and (max-width: 600px) {

._H1 {
        font-size: 40px;
    } 

}