Returns the `top`, `left`, `width`, `height` relative to the `body`'s coordinates. It is an interface for `this.node.getBoundingClientRect()`

```javascript
var parent = el('div');

parent.appendTo(document.body);

parent.offset();
/* -> {
        height : [Number],
        left : [Number],
        top : [Number],
        width : [Number]
      }
*/
```