web/web_x2many_delete_all/templates/assets.xml

<?xml version="1.0" encoding="UTF-8"?>
<!-- Copyright 2016 Onestein
     License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl). -->

<odoo>
    <template id="assets_backend" inherit_id="web.assets_backend">
        <xpath expr=".">
            <script type="text/javascript"
                    src="/web_x2many_delete_all/static/src/js/web_x2many_delete_all.js"/>
            <link rel="stylesheet"
                  href="/web_x2many_delete_all/static/src/css/web_x2many_delete_all.css"/>
        </xpath>
    </template>
</odoo>