soapoperator on "[Twenty Thirteen child theme] Genericons with css method are well shown"

Hello,

I am building a child theme for the Twenty Thirteen theme.

I have an issue with the genericon.
When i use the html methode, it work perfectly. At the contraring, with the css method, it shows an ugly font.

For exemple on this sample page: here

I use for genericon-tumblr:
Copy CSS
content: '\f214';
> it doesn't work!

I use for genericon-draggable:
Copy Html
<span class="genericon genericon-draggable"></span>
> it works perfectly!

Maybe i missed something.
Could it be a conflit with another font or plugin?
Any help will be appreciated.

Thank you in advance,
jB