For more detail about possible style overrides, see the Reference page.
You can customize styles for almost all the visual elements throughout the Dromo Uploader. Upload screen Set header screen Matching screen Clean data screen Review screen

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Basic Example​

In this example, we change the text color to dark gray, the primary button to blue, and the secondary button to red. 
const settings = {
  styleOverrides: {
    global: {
      textColor: "#394b59",
      customFontURL: "https://fonts.googleapis.com/css2?family=Open+Sans&display=swap",
      customFontFamily: "'Open Sans', sans-serif"
    },
    primaryButton: {
      borderRadius: "0.25rem",
      backgroundColor: "#1a4a7a",
      textColor: "#ffffff",
      border: "1px solid #1a4a7a",
      hoverBackgroundColor: "#006bef",
      hoverTextColor: "#ffffff",
      hoverBorder: "1px solid #006bef"
    },
    secondaryButton: {
      borderRadius: "0.25rem",
      backgroundColor: "#b0276b",
      textColor: "#ffffff",
      border: "1px solid #b0276b",
      hoverBackgroundColor: "#5c656d",
      hoverTextColor: "#fffff",
      hoverBorder: "1px solid #5c656d"
    }
  }
}