Question

I’d like to tell the browser to assign certain CSS classes to elements matching a particular selector. Can I do it with pure CSS and if yes, how?

Example: I want all the h5 elements inside a div with id sidebar to have the class ui-corners-all

Answer 1

No, that isn’t possible with pure CSS.

Only with JavaScript:

// jQuery
$("h5").addClass("ui-corners-all");

// Pure JavaScript
var elements = document.getElementsByTagName("h5");
for (var i=0; i<elements.length; i++)
{
  var el = elements[i];      
  el.setAttribute( "class", el.getAttribute("class") + " ui-corners-all" );
}