I´m developing a responsive website where I use the <details> <summary> elements to show aditional information in the services section. 
How can I change the details "open" attribute when the window width > 768px ? 
It´s possible to do only with css?
Here is the html code:
<section id="services">
    <section>
        <details>
            <summary>info</summary>
            <p>A paragraph with especific information</p>
        </details>
   </section>
</section>  
I can use a javascript code like this, but prefer css:
  var desplegable = $("#services section details");
if ($(window).width() > 768) {
    if (desplegable.attr("open") != "open"){ 
        desplegable.attr('open','true');
    }
}
Any idea? Thanks
The Spetec: http://www.whatwg.org/specs/web-apps/current-work/multipage/interactive-elements.html#the-details-element