To load assets in the Point of Sale application, follow these steps:

1. Add a new SCSS file at /pos_demo/static/src/scss/pos_demo.scss and insert the following code:

.pos .pos-content {
    .price-tag {
        background: #00abcd;
        width: 100%;
        right: 0;
        left: 0;
        top:0;
    }
}

2. Add a JavaScript file at /pos_demo/static/src/js/pos_demo.js and add the following:

console.log('Point of Sale JavaScript loaded');

3. Register these JavaScript and SCSS files into the point_of_sale assets:

<?xml version="1.0" encoding="utf-8"?>
<odoo>
    <data>
        <template id="assets" inherit_id="point_of_sale.assets">
            <xpath expr="." position="inside">
                <script type="text/JavaScript"
                        src="/pos_demo/static/src/js/pos_demo.js"/>
                <link rel="stylesheet"
                      href="/pos_demo/static/src/scss/pos_demo.scss"/>
            </xpath>
        </template>
    </data>
</odoo>

Install the pos_demo module. To see your changes in action, open the point-of-sale session from the Point of Sale|Dashboard menu.