The center of the pie chart relative to the plot area. Can be
percentages or pixel values. The default behaviour (as of 3.0) is to
center the pie so that all slices and data labels are within the plot
area. As a consequence, the pie may actually jump around in a chart
with dynamic values, as the data labels move. In that case, the
center should be explicitly set, for example to ["50%", "50%"].