How to use the @uifabric/utilities.merge function in @uifabric/utilities

if (!theme.palette || !theme.palette.accent) {
    newPalette.accent = newPalette.themePrimary;
  }

  // mix in custom overrides with good slots first, since custom overrides might be used in fixing deprecated slots
  let newSemanticColors = {
    ..._makeSemanticColorsFromPalette(newPalette, !!theme.isInverted, depComments),
    ...theme.semanticColors
  };

  let defaultFontStyles: IFontStyles = { ...DefaultFontStyles };

  if (theme.defaultFontStyle) {
    for (const fontStyle of Object.keys(defaultFontStyles)) {
      defaultFontStyles[fontStyle] = merge({}, defaultFontStyles[fontStyle], theme.defaultFontStyle);
    }
  }

  if (theme.fonts) {
    for (const fontStyle of Object.keys(theme.fonts)) {
      defaultFontStyles[fontStyle] = merge({}, defaultFontStyles[fontStyle], theme.fonts[fontStyle]);
    }
  }

  return {
    palette: newPalette,
    fonts: {
      ...defaultFontStyles
    },
    semanticColors: newSemanticColors,
    isInverted: !!theme.isInverted,

let newSemanticColors = {
    ..._makeSemanticColorsFromPalette(newPalette, !!theme.isInverted, depComments),
    ...theme.semanticColors
  };

  let defaultFontStyles: IFontStyles = { ...DefaultFontStyles };

  if (theme.defaultFontStyle) {
    for (const fontStyle of Object.keys(defaultFontStyles)) {
      defaultFontStyles[fontStyle] = merge({}, defaultFontStyles[fontStyle], theme.defaultFontStyle);
    }
  }

  if (theme.fonts) {
    for (const fontStyle of Object.keys(theme.fonts)) {
      defaultFontStyles[fontStyle] = merge({}, defaultFontStyles[fontStyle], theme.fonts[fontStyle]);
    }
  }

  return {
    palette: newPalette,
    fonts: {
      ...defaultFontStyles
    },
    semanticColors: newSemanticColors,
    isInverted: !!theme.isInverted,
    disableGlobalClassNames: !!theme.disableGlobalClassNames,
    spacing: {
      ...DefaultSpacing,
      ...theme.spacing
    },
    effects: {