Here is an example of how you can use the LevelToSyslogSeverity 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.LevelToSyslogSeverity;
import org.slf4j.LoggerFactory;

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

    // Set the logger level to ERROR
    logger.setLevel(Level.ERROR);

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

    // Convert the logger level to a syslog severity
    int syslogSeverity = LevelToSyslogSeverity.convert(context, Level.ERROR);
    System.out.println(syslogSeverity);  // prints 3
  }
}

The LevelToSyslogSeverity class is a utility class that provides a method for converting a logback Level to a syslog severity. The convert method takes a LoggerContext and a Level as arguments, and returns an integer representing the syslog severity.

In this example, we use the convert method to convert the Level.ERROR constant to a syslog severity. The syslog severity values are as follows:

0: Emergency
1: Alert
2: Critical
3: Error
4: Warning
5: Notice
6: Informational
7: Debug