Pie: Donut Hole
`%%{init: {"pie": {"donutHole": 0.5}}}%%` cuts a hole of half the radius in the SVG; Mermaid keeps the labels where they were. The ASCII bar chart has no centre to cut, so it is unchanged.
pie-donut-hole.mmd
%%{init: {"pie": {"donutHole": 0.5}}}%%
pie title Pets adopted by volunteers
"Dogs" : 386
"Cats" : 85
"Rats" : 15