How to use the victory.VictoryTheme.grayscale function in victory

get theme() {
    const fontSize = 10;
    return merge({}, VictoryTheme.grayscale, {
      chart: { padding: { top: 30, bottom: 30, left: 50, right: 50 } },
      axis: {
        // Default theme applies to both x & y axes.
        style: {
          axis: {
            stroke: "white"
          },
          axisLabel: {
            fill: "white",
            padding: -15
          },
          grid: {
            stroke: "white",
            strokeWidth: "1px",
            opacity: 0.086
          },

get theme() {
    const fontSize = 10;
    const textColor = "white";
    return merge({}, VictoryTheme.grayscale, {
      chart: { padding: { top: 15, bottom: 30, left: 50, right: 0 } },
      independentAxis: {
        style: {
          axis: { stroke: "none" },
          axisLabel: { fontSize, padding: 15, fill: textColor },
          tickLabels: { fontSize: 0, padding: 0 },
          grid: {
            stroke: "none",
            fill: "none"
          }
        }
      },
      dependentAxis: {
        style: {
          axis: { stroke: "none" },
          tickLabels: { fontSize, fill: textColor },