ly equal to the distance that 'middle'
                 causes the centerpoint of the image to be from the baseline. Since the centerpoint
                 is 1em above the bottom of the image, that means the bottom of the image has to be
                 moved -0.6em so that it is at the same position as it would be with 'vertical-align'
                 set to 'middle'. The bottom of the image is a further 0.6em+1em-1.5em from the bottom
                 margin edge of the whole replaced element, which is