It seems that the pivot table integration does not allow to size C3 charts to use the available space. According to the documentation and this example: https://jsfiddle.net/nicolaskruchten/gq6w05j8/ the size of the chart should follow the size of the container element if not explicitly set. In the given example this works fine.
Description of the bug or enhancement
Taken from https://www.cuba-platform.com/discuss/t/c3-charts-in-pivot-table-cannot-be-sized-to-100/6794
AR: