mail-addons/mail_attachment_popup/views/mail_attachment_popup_template.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <template id="assets_backend" name="account assets" inherit_id="web.assets_backend">
            <xpath expr="." position="inside">
                <link rel="stylesheet" href="/mail_attachment_popup/static/src/css/jquery.arcticmodal.css"/>
                <link rel="stylesheet" href="/mail_attachment_popup/static/src/css/simple.css"/>
                <link rel="stylesheet" href="/mail_attachment_popup/static/src/css/styles.css"/>
                <script type="text/javascript" src="/mail_attachment_popup/static/lib/js/jquery.arcticmodal.js"></script>
            </xpath>
        </template>
    </data>
</openerp>