I using odoo 15 and placed the css in \project_km\static\src\css\project_km.css

In my manifest i have add:

'assets': {
'web.assets_backend': [
'project_km/static/src/css/project_km.css',
]
},

But in my inherited view the setting of the class is not working:

xpath expr="//page[@name='settings']" position="after">
page name="used_materials_page" string="Mustermaterial">
group>
field name="used_material" class="kmf_material_column">
tree>
field name="product_uom_qty"/>
field name="product_id"/>




 

Here is my content of css:

.kmf_material_column
{
width: 200px;
}