<NME> test-container-styles.css
<BEF> #ember-testing-container {
  position: fixed;
  background: white;
  bottom: 0;
  right: 0;
  width: 640px;
  height: 384px;
  overflow: auto;
  z-index: 9999;
  border: 1px solid #ccc;
}
#ember-testing {
  zoom: 50%;
}

<MSG> Merge pull request #459 from nickschot/fix-testing-container-leakage

Prevent leakage of position fixed elements from the testing container
<DFF> @@ -8,6 +8,9 @@
   overflow: auto;
   z-index: 9999;
   border: 1px solid #ccc;
+
+  /* Prevent leaking position fixed elements outside the testing container */
+  transform: translateZ(0);
 }
 #ember-testing {
   zoom: 50%;

Merge pull request #459 from nickschot/fix-testing-container-leakage