web/web_fullscreen/views/web_fullscreen_view.xml

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