How to add css and js files to Odoo ? (Odoo 14 and previous versions)

assets.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>
    <data>
        <template id="assets_backend" name="doc assets" inherit_id="web.assets_backend">
            <xpath expr="." position="inside">
                <link rel="stylesheet" href="/your_module/static/src/css/your_css.css"/>
                <script type="text/javascript" src="/your_module/static/src/js/your_js.js"/>
            </xpath>
        </template>
    </data>
</odoo>