paper.localToClientRect(rect)

Transform the rectangle rect defined in local coordinate system to the client coordinate system.

var bbox = element.getBBox();
var clientRect1 = paper.localToClientRect(bbox);
 // alternative method signature
var clientRect2 = paper.localToClientRect(bbox.x, bbox.y, bbox.width, bbox.height);
// Draw an HTML rectangle above the element.
var div = document.createElement('div');
div.style.position = 'fixed';
div.style.background = 'red';
div.style.left = clientRect1.x + 'px';
div.style.top = clientRect1.y + 'px';
div.style.width = clientRect1.width + 'px';
div.style.height = clientRect1.height + 'px';
paper.el.appendChild(div);