How to use the @nivo/calendar.CalendarDefaultProps.monthBorderColor function in @nivo/calendar

key: 'monthBorderWidth',
        flavors: ['svg', 'api'],
        help: 'width of month borders.',
        type: 'number',
        required: false,
        defaultValue: defaults.monthBorderWidth,
        controlType: 'lineWidth',
        group: 'Months',
    },
    {
        key: 'monthBorderColor',
        flavors: ['svg', 'api'],
        help: 'color to use for months border.',
        type: 'string',
        required: false,
        defaultValue: defaults.monthBorderColor,
        controlType: 'colorPicker',
        group: 'Months',
    },
    {
        key: 'monthLegend',
        help: `can be used to customize months label, returns abbreviated month name (english) by default. This can be used to use a different language`,
        type: '(year: number, month: number, date: Date) => string | number',
        required: false,
        group: 'Months',
    },
    {
        key: 'monthLegendPosition',
        help: 'defines month legends position.',
        type: `'before' | 'after'`,
        required: false,
        defaultValue: defaults.monthLegendPosition,