mail-addons/mail_private/template.xml

<?xml version="1.0" encoding="utf-8" ?>
<!--Copyright 2016 x620 <https://github.com/x620>
    License MIT (https://opensource.org/licenses/MIT).-->
<odoo>
    <template
        id="assets_backend"
        name="mail_private_assets_backend"
        inherit_id="web.assets_backend"
    >
        <xpath expr="." position="inside">
            <link
                rel="stylesheet"
                href="/mail_private/static/src/css/mail_private.css"
            />
            <script
                type="text/javascript"
                src="/mail_private/static/src/js/mail_private.js"
            />
            <script
                type="text/javascript"
                src="/mail_private/static/src/js/test_private.js"
            />
        </xpath>
    </template>
</odoo>