--- a/devtools/client/shared/widgets/Spectrum.js
+++ b/devtools/client/shared/widgets/Spectrum.js
@@ -128,28 +128,17 @@ Spectrum.rgbToHsv = function (r, g, b, a
       case b: h = (r - g) / d + 4; break;
     }
     h /= 6;
   }
   return [h, s, v, a];
 };
 
 Spectrum.getOffset = function (el) {
-  let curleft = 0, curtop = 0;
-  if (el.offsetParent) {
-    while (el) {
-      curleft += el.offsetLeft;
-      curtop += el.offsetTop;
-      el = el.offsetParent;
-    }
-  }
-  return {
-    left: curleft,
-    top: curtop
-  };
+  return el.getBoundingClientRect();
 };
 
 Spectrum.draggable = function (element, onmove, onstart, onstop) {
   onmove = onmove || function () {};
   onstart = onstart || function () {};
   onstop = onstop || function () {};
 
   let doc = element.ownerDocument;