ll-change: opacity; transform: translateZ(0px); opacity: 0;'),
              'backgroundRearLayer when progress = 0');

          container._updateScrollState(container.offsetHeight);

          assert.isTrue(sameCSS(container.$.backgroundFrontLayer,
              'will-change: opacity; transform: translateZ(0px); opacity: 0;'),
              'backgroundFrontLayer when progress = 1');

          assert.isTrue(sameCSS(container.$.backgroundRearLayer,
              'will-change: opacity; transform: translateZ