In Odoo 16, the assets management system has changed. The old web.assets_backend no longer exists. Instead, Odoo 16 uses:

• web._assets_backend → For the Community edition
• web._assets_enterprise → For the Enterprise edition

So, if we try to inherit web.assets_backend, Odoo will throw an error because it does not exist.

Solution:

✅ 1. Update the header.xml file

Modify the inherit_id in your XML file:

xml
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<?xml version="1.0" encoding="UTF-8"?>
<odoo>
    <template id="assets_backend_inherit" inherit_id="web._assets_backend" name="Custom Backend Assets">
        <xpath expr="." position="inside">
            <link rel="stylesheet" type="text/css" href="/custom_theme/static/src/css/theme.css"/>
        </xpath>
    </template>
</odoo>

If you are using Odoo Enterprise, replace web._assets_backend with web._assets_enterprise.

✅ 2. Correctly Define Assets in __manifest__.py

In Odoo 16, assets are defined inside the assets dictionary. Update your __manifest__.py:

python
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'assets': {
    'web._assets_backend': [
        '/custom_theme/static/src/css/theme.css',
    ],
},

Again, for Enterprise Edition, use web._assets_enterprise.


Restart odoo

Hi Ahamed,

It seems that you are trying to append the stylesheet.

Do you mind to try the steps below? I took reference from "crm" module.

1. Remove the xml, don't append through template inheritance.
2. Inside the manifest.py, remove the slash(/) before "custom_theme"