Here is an example of using the DefaultCssBuilder class from the logback-classic library in Java:

import ch.qos.logback.core.html.CssBuilder;

public class LogbackExample {
    public static void main(String[] args) {
        CssBuilder cssBuilder = new DefaultCssBuilder();
        String css = cssBuilder.toString();
        System.out.println(css);
    }
}

This example creates an instance of DefaultCssBuilder class and calls its toString() method to generate a string representation of the default CSS that can be used in an HTML-based log event layout.

DefaultCssBuilder class is a default implementation of CssBuilder that generates a basic CSS style sheet that can be used with the HTMLLayout and other logback components that generate HTML output.

You can use the string output generated by this class, and include it in your layout.xml file in order to display the logs in proper format in HTML.

You can also customize the generated CSS by creating custom implementation of CssBuilder and providing your own CSS formatting rules.

Please be aware that this is a very basic example, in real-world scenarios you will probably want to customize the CSS and use it with a log layout that produces HTML.