Most of the files are

  :Copyright: This stylesheet has been placed in the public domain.
  <!-- Copyright 2017 ACSONE SA/NV
  <!-- Copyright 2019 ACSONE SA/NV
  <!-- © 2016 Akretion (Alexis de Lattre <alexis.delattre@akretion.com>) -->
  Copyright 2015-2016 Akretion - Alexis de Lattre
  Copyright 2017 Camptocamp SA
  Copyright 2017 Creu Blanca
  Copyright 2018 Tecnativa - Pedro M. Baeza
  Copyright 2019 ACSONE SA/NV
  Copyright 2019 Tecnativa - Pedro M. Baeza
  © 2009 EduSense BV (<http://www.edusense.nl>)
  © 2011-2013 Therp BV (<https://therp.nl>)
  © 2013-2016 Akretion (https://www.akretion.com)
  © 2014 Serv. Tecnol. Avanzados - Pedro M. Baeza
  © 2014-2015 ACSONE SA/NV (<https://acsone.eu>)
  © 2014-2016 Akretion (Alexis de Lattre <alexis.delattre@akretion.com>)
  © 2014-2016 Tecnativa - Pedro M. Baeza
  © 2015-2016 Akretion (<https://www.akretion.com>)
  © 2015-2016 Akretion (https://www.akretion.com/)
  © 2015-2016 Akretion - Alexis de Lattre <alexis.delattre@akretion.com>
  © 2016 Akretion (<https://www.akretion.com>)
  © 2016 Akretion (Alexis de Lattre - alexis.delattre@akretion.com)
  © 2016 Akretion (Alexis de Lattre <alexis.delattre@akretion.com>)
  © 2016 Akretion (https://www.akretion.com/)
  © 2016 Aselcis (<https://www.aselcis.com>).
  © 2017 Creu Blanca
  Copyright 2018 Flectra Community

Many files also contain contributions from third
parties. In this case the original copyright of
the contributions can be traced through the
history of the source version control system.

When that is not the case, the files contain a prominent
notice stating the original copyright and applicable
license, or come with their own dedicated COPYRIGHT
and/or LICENSE file.