Alignment of the legend.
Can be one of the following:
start, center, end. Alignments are relative to the style -- vertical or horizontal -- of the legend.
For example, in a 'right' legend, 'start' and 'end' are at the top and bottom, respectively; for a 'top' legend, 'start' and 'end' would be at the left and right of the area, respectively. The default value depends on the legend's position. For 'bottom' legends, the default is 'center'; other legends default to 'start'.