account-financial-tools/account_spread_cost_revenue/templates/assets.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>

    <template id="assets_backend" name="account spread" inherit_id="web.assets_backend">
        <xpath expr="." position="inside">
            <link rel="stylesheet" href="/account_spread_cost_revenue/static/src/scss/account_spread.scss"/>
            <script type="text/javascript" src="/account_spread_cost_revenue/static/src/js/account_spread.js"></script>
        </xpath>
    </template>

</odoo>