Configuration File
Add a file named custom-sidebar-config.yaml into your <config directory>/www/ directory. It is recommendable that you copy the example custom-sidebar-config.yaml file and modify it to match your needs. Begin with the simplest configuration and start to extend it step by step, in that way if you suffer any issue, it is easy to identify with which code block it started.
info
Delete or edit the id parameter of the example configuration. It is there just to detect if you have not edited the example configuration.
tip
If you want to check an extensive sidebar configuration which uses custom styles, variables and templates, check @Mariusthvdb's custom-sidebar-config.yaml.