eiru_theme/views/eiru_assets_backend.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <template id="eiru_theme.assets_backend" name="Eiru Assets Backend" inherit_id="web.assets_backend">
            <xpath expr="." position="inside">
                <link rel="stylesheet" href="/eiru_theme/static/src/css/backend/theme.css" />
            </xpath>
        </template>
    </data>
</openerp>