Here is an example of how you can use the ClassicConstants class from the logback.classic package:

import ch.qos.logback.classic.Level;
import ch.qos.logback.classic.Logger;
import ch.qos.logback.classic.LoggerContext;
import ch.qos.logback.classic.util.ClassicConstants;
import org.slf4j.LoggerFactory;

public class MyClass {
  public static void main(String[] args) {
    // Get the logger
    Logger logger = (Logger) LoggerFactory.getLogger(MyClass.class);

    // Get the logger context
    LoggerContext context = logger.getLoggerContext();

    // Set the root logger level using the ClassicConstants class
    context.getLogger(ClassicConstants.ROOT_LOGGER_NAME).setLevel(Level.ERROR);

    // Set the logger level using the ClassicConstants class
    logger.setLevel(Level.DEBUG);
  }
}

The ClassicConstants class is a utility class that provides constants used in the logback.classic package. In this example, we use the ROOT_LOGGER_NAME constant to set the root logger level and the DEBUG constant to set the logger level.

The ROOT_LOGGER_NAME constant is a string representing the name of the root logger, which is "ROOT". The DEBUG constant is an instance of the Level class representing the debug log level.