#ember-testing-container {
  position: relative;
  background: white;
  bottom: 0;
  right: 0;
  width: 640px;
  height: 384px;
  overflow: auto;
  z-index: 98;
  border: 1px solid #ccc;
  margin: 0 auto;

  /* Prevent leaking position fixed elements outside the testing container */
  transform: translateZ(0);
}

#ember-testing-container.full-screen {
  width: 100%;
  height: 100%;
  overflow: auto;
  z-index: 98;
  border: none;
}

#ember-testing {
  width: 200%;
  height: 200%;
  transform: scale(0.5);
  transform-origin: top left;
}

.full-screen #ember-testing {
  position: absolute;
  width: 100%;
  height: 100%;
  transform: scale(1);
}

#ember-testing-container {
  position: relative;

  background-color: #fff;
  background-image:
    linear-gradient(45deg, #eee 25%, transparent 25%, transparent 75%, #eee 75%, #eee),
    linear-gradient(45deg, #eee 25%, transparent 25%, transparent 75%, #eee 75%, #eee);
  background-position: 0 0, 10px 10px;
  background-size: 20px 20px;

  bottom: 0;
  right: 0;
  width: 640px;
  height: 384px;
  overflow: auto;
  z-index: 98;
  border: 1px solid #ccc;
  margin: 0 auto;

  /* Prevent leaking position fixed elements outside the testing container */
  transform: translateZ(0);
}

#ember-testing-container.full-screen {
  width: 100%;
  height: 100%;
  overflow: auto;
  z-index: 98;
  border: none;
}

#ember-testing {
  width: 200%;
  height: 200%;
  transform: scale(0.5);
  transform-origin: top left;
}

.full-screen #ember-testing {
  position: absolute;
  width: 100%;
  height: 100%;
  transform: scale(1);
}

Use checkerboard pattern for testing container background
Use checkerboard pattern for testing container background

This changes the default background of the `#ember-testing-container` from purely white to a slight checkerboard pattern to make it more obvious what rendered components have a transparent vs. a white background.
