I think it would be handy to have the legend box anchored by a point you choose. For instance, if your legend was located in the top right hand corner, you could make the anchor point the top right corner of the legend box. Now if you add themes or the description of one becomes longer or shorter it will change the size of the box without leaving a gap or overlapping the border (it would expand or contract from that anchor point inward toward the inside of the TB).
