PB responsive design

Hello,

I made a child theme to get this website : http://www.cedricgournay.com. I know this website will be hard to get responsive but my client knows it.

When I let the by default mobile css, it’s not really nice, so I commented it (no child css for the moment, I just wanted to understand how it works) and it’s better.
If you have a look on the website on an iphone, horizontally to this page : http://www.cedricgournay.com/design-global/, you can see that design global is too big.

So in the style-mobile.css (the theme one for the moment), I tried to write

@media (max-width: 480px) {
body-mobile #primary .text-vertical-sb h1 {font-size:8px;}
}

But nothing happens. Can anyone help me understanding what’s wrong?
Thanks in advance !