How to use $A.util.toggleClass in Salesforce Lightning Components?

To change styles dynamically, use $A.util.toggleClass() or $A.util.addClass(),$A.util.removeClass().
Use $A.util.toggleClass() for component instead of a DOM element.

//toggleCss.cmp
<aura:component>
   <div aura:id=”changeIt”>Change Me!</div><br />
   <ui:button press=”{!c.applyCSS}” label=”Add Style” />
   <ui:button press=”{!c.removeCSS}” label=”Remove Style” />
</aura:component>

//toggleCssController.js
({
   applyCSS: function(cmp, event) {
      var cmpTarget = cmp.find(‘changeIt’);
      $A.util.addClass(cmpTarget, ‘changeMe’);
   },
   removeCSS: function(cmp, event) {
      var cmpTarget = cmp.find(‘changeIt’);
      $A.util.removeClass(cmpTarget, ‘changeMe’);
   }
})

//toggleCss.css
.THIS.changeMe {
    background-color:yellow;
    width:200px;
}