How to use the @nivo/stream.StreamDefaultProps.fillOpacity function in @nivo/stream

},
    {
        key: 'colors',
        help: 'Defines how to compute line color.',
        type: 'string | Function',
        required: false,
        defaultValue: defaults.colors,
        controlType: 'ordinalColors',
        group: 'Style',
    },
    {
        key: 'fillOpacity',
        help: 'Layers fill opacity.',
        type: 'number',
        required: false,
        defaultValue: defaults.fillOpacity,
        controlType: 'opacity',
        group: 'Style',
    },
    {
        key: 'borderWidth',
        help: 'Width of layer border.',
        type: 'number',
        required: false,
        defaultValue: defaults.borderWidth,
        controlType: 'lineWidth',
        group: 'Style',
    },
    {
        key: 'borderColor',
        description: `
            How to compute border color,