pos/pos_product_template/view/view.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright (C) 2014-Today Akretion (https://www.akretion.com)
     @author Sylvain LE GAL (https://twitter.com/legalsylvain)
     License LGPL-3.0 or later (https://www.gnu.org/licenses/lgpl). -->
<odoo>
    <!-- Add: JS Files -->
    <template id="assets_backend" name="point_of_sale assets2" inherit_id="point_of_sale.assets">
        <xpath expr="." position="inside">
            <script type="text/javascript" src="/pos_product_template/static/src/js/ppt.js"></script>
        </xpath>
    </template>

    <!-- Add: CSS Files -->
    <template id="index" name="pos_product_template assets" inherit_id="point_of_sale.assets">
        <xpath expr="//link[@id='pos-stylesheet']" position="after">
            <link rel="stylesheet" href="/pos_product_template/static/src/css/ppt.css" id="pos_product_template-stylesheet"/>
        </xpath>
    </template>
</odoo>