Hi,

To change the font size of all reports you need to inherit the report_layout.

You can add the font style for a div with id "wrapwrap" inside the template.

example:

 <template id="inherit_report_layout"
inherit_id="web.report_layout">
        <xpath expr="//div[@id='wrapwrap']"
               position="attributes">

               <attribute name="style">font-size:10px;</attribute>
        </xpath>

</template>

Hope its helpful

Hope it helps