made a new report with a special format 420mm x 210mm. I try to position boxes inside my report using divs with css margins given in millimeters. Howevers, I noticed that when I specify 420mm in the css, the output in the pdf is not 420mm, but something smaller. I just made the following :

<template id="test">
    <t t-call="report.html_container">
        <t t-foreach="docs" t-as="o">
            <div class="test page">
            </div>
        </t>
    </t>
</template>

<template id="test_style" inherit_id="report.style">
    <xpath expr=".">
        <t>
                .test.page {
                        width: 420mm;
                        height: 210mm;
                        background-color: red;
                    }
        </t>
    </xpath>
</template>

The output is the following, the box does not fill the page. The page size is correct (420x210):

So my question is how can I set the position in millimeters and it would be exact for generating the pdf ?