.css(), the values ​like "+=10%" are now managed (like .animate())

Hi :)

Actually when we make:

    $this.animate({width: "+=10%"}, 500);

it's work fine, the value is converted into percentage BUT if we write:

    $this.css("width", "+=10%");

We don't have the same behavior...
The .css() function doesn't look the unity, it's "px" every time.