How to use the typography.caption.fontSize function in typography

color: "${theme["colorScheme.textColor"]}"
      },
      h5: {
        fontSize: "${theme["density.fontSizes.small"]}",
        fontWeight: "${theme["basics.fontWeights.medium"]}",
        lineHeight: "${theme["basics.lineHeights.mediumSmall"]}",
        color: "${theme["colorScheme.textColor"]}"
      },
      h6: {
        fontSize: "${theme["density.fontSizes.small"]}",
        fontWeight: "${theme["basics.fontWeights.medium"]}",
        lineHeight: "${theme["basics.lineHeights.mediumSmall"]}",
        color: "${theme["colorScheme.textColor"]}"
      },
      caption: {
        fontSize: "${theme["typography.caption.fontSize"]}",
        lineHeight: "${theme["typography.caption.lineHeight"]}",
        color: "${theme["typography.caption.color"]}",
        textAlign: "left"
      }
    },
    palette: {
      background: {
        default: "${themeBackground}",
        paper: "${paperBackground}"
      },
      primary: {
        main: "${theme["colorScheme.accentColor"]}"
      },
      secondary: {
        main: "${theme["colorScheme.accentColor"]}"
      }