The shape-outside in this test is a 2x2 image with only the upper left pixel set. The shape element's margin-box is and the the shape-margin is big enough (is greater than 150 * sqrt(2)) so that the shape-margin boundary extends beyond the margin-box's bounds. The shape-outside boundary is clipped to the margin-box, so it's as if the shape-outside was equal to the margin-box.