pos/pos_meal_voucher/views/templates.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--
Copyright (C) 2020 - Today: GRAP (http://www.grap.coop)
@author: Sylvain LE GAL (https://twitter.com/legalsylvain)
License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
-->

<odoo>
    <template id="assets" inherit_id="point_of_sale.assets">
        <xpath expr="." position="inside">
             <link rel="stylesheet" href="/pos_meal_voucher/static/src/css/pos_meal_voucher.css"/>
            <script type="text/javascript" src="/pos_meal_voucher/static/src/js/models.js"></script>
            <script type="text/javascript" src="/pos_meal_voucher/static/src/js/screens.js"></script>
        </xpath>
    </template>
</odoo>