Hi,

Please refer this

https://www.odoo.com/forum/help-1/including-css-file-to-odoo-115854

Muhammed Ali M - iWesabe

Create one static module in your module ,inside the static create css folder,and inside css create css file.

example:

And now you create one xml file inside views,in that xml file create code like this,

ex:

<?xml version="1.0" encoding="UTF-8"?>
<odoo>
    <data>
        <template id="assets_backend" name="sale_order_footer assets" inherit_id="web.assets_backend">
            <xpath expr="." position="inside">
                <link rel="stylesheet" href="/module _name/static/src/css/sale_order_footer.css"/>
            </xpath>
        </template>

</data>

</odoo>
       
Thats SOLVE, Now YOU CHECK NEW CHANGES