Style for Region

# style_region.js

var chart = c3.generate({ data: { columns: [ ['sample', 30, 200, 100, 400, 150, 250] ] }, regions: [ {start:0, end:1}, {start:2, end:4, class:'foo'} ] });

# style_region.css

.c3-region-0 {
 fill: red;
}
.c3-region.foo {
 fill: green;
}