Trying to convert serinity index.html file to pdf, but css gui images are not coming, only page is getting opened

used these two lines of code and dependencies which i added

HtmlConverter.convertToPdf(new FileInputStream("./target/site/serenity/index.html"), new FileOutputStream("./BatchRunFiles/index-to-pdf.pdf"));

 <dependency>
            <groupId>com.itextpdf</groupId>
            <artifactId>itext7-core</artifactId>
            <version>7.1.9</version>
        </dependency><!-- iText pdfHTML add-on -->
        <dependency>
            <groupId>com.itextpdf</groupId>
            <artifactId>html2pdf</artifactId>
            <version>2.1.6</version>
        </dependency>