Hi, I am a newbie in Odoo development, we use odoo v16.0.

We want to be able to change the color of the backend by using a custom module. We searched the web and found some suggestions.

We have a custom module folder structure with __manifest__.py

My manifest file:

{
​'name': 'Better looking backend theme',
​'summary': 'Better Theme Backend',
​'description': 'Better backend theme',
​'category': 'Theme/Creative',
​'depends': ['base'],
​'author': 'Mickey Mouse',
​'data': [
​ ​'views/assets.xml',
​],
​'assets': {
​ ​"web.assets_backend": [
​ ​ ​'inx_backend_theme/static/src/css/theme.css',
​ ​ ​],
​ ​},
​ ​'images': [
​ ​ ​'static/description/icon.png',
​ ​​],
​ ​'installable': True,
​ ​'auto_install': False,
​ ​'application': True,
}



My assets.xml file

	​
	​	​
	​	​	​	​
	​	​	​	​
	​	​	​
	​	​
	​

The css file

.o_main_navbar {
	​background-color: #0071ce !important;
}

This is the log:

The log when attempting to Activate the module:
Traceback (most recent call last):
  File "/odoo/odoo/tools/cache.py", line 85, in lookup
    r = d[key]
        ~^^^^^
  File "", line 2, in __getitem__
  File "/odoo/odoo/tools/func.py", line 87, in locked
    return func(inst, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/odoo/odoo/tools/lru.py", line 34, in __getitem__
    a = self.d[obj]
        ~~~~~~^^^^^
KeyError: ('ir.model.data', , 'web.assets_backend')

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/odoo/odoo/tools/convert.py", line 698, in _tag_root
    f(rec)
  File "/odoo/odoo/tools/convert.py", line 676, in _tag_template
    return self._tag_record(record)
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/odoo/odoo/tools/convert.py", line 568, in _tag_record
    f_val = self.id_get(f_ref, raise_if_not_found=nodeattr2bool(rec, 'forcecreate', True))
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/odoo/odoo/tools/convert.py", line 681, in id_get
    res = self.model_id_get(id_str, raise_if_not_found)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/odoo/odoo/tools/convert.py", line 687, in model_id_get
    return self.env['ir.model.data']._xmlid_to_res_model_res_id(id_str, raise_if_not_found=raise_if_not_found)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/odoo/odoo/addons/base/models/ir_model.py", line 2002, in _xmlid_to_res_model_res_id
    return self._xmlid_lookup(xmlid)[1:3]
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "", line 2, in _xmlid_lookup
  File "/odoo/odoo/tools/cache.py", line 90, in lookup
    value = d[key] = self.method(*args, **kwargs)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/odoo/odoo/addons/base/models/ir_model.py", line 1995, in _xmlid_lookup
    raise ValueError('External ID not found in the system: %s' % xmlid)
ValueError: External ID not found in the system: web.assets_backend

The above exception was the direct cause of the following exception:

When trying to Activate the module I get the above error. Again, we run Odoo CE v16.0

We need help to understand what's wrong

Thanks