Font-family and color different browsers

Hello ! (sorry for my english, i’m french)
First, thank you for your theme, it’s awesome !
But i have a problem (of course, if not i will not contact you ;-))
I’m working on it after i’ve created a child theme (i’m in localhost). I want my own font-family (the girl next door, google fonts, for instance) and my own color for the text.
I’m using Firefox and everything i’ve changed in the css works really fine so for firefox it’s ok. But and that’s the problem (for my future visitors) : in google chrome, opera, and IE (well forget about IE, lol), nothing of these changes are applied (like if the theme parent css is stronger than my child css for these browsers).
I need some help to resolve the problem, please.