When the mouse enters the avatar then set the style class to the 'over' style class (solid blue) and when the mouse leaves set it to the 'not-over' style classes (dotted blue).

$proto('#avatar', {
  Mouseover: {
    onMouseover: {
      ReplaceClass: {
        removeClass: 'not-over',
        addClass: 'over'
      }
    }
  },
  Mouseout: {
    onMouseout: {
      ReplaceClass: {
        removeClass: 'over',
        addClass: 'not-over'
      }
    }
  }
});

Toggle Style Class on Mouseout and Mouseover