web/web_dialog_size/static/src/xml/web_dialog_size.xml

<?xml version="1.0" encoding="UTF-8"?>
<templates id="template" xml:space="preserve">
    <t t-extend="Dialog">
        <t t-jquery="button.close" t-operation="inner">
            <i class="fa fa-close" />
        </t>
        <t t-jquery="button.close" t-operation="before">
            <button type="button" class="dialog_button_extend close"><i class="fa fa-expand" /></button>
            <button type="button" class="dialog_button_restore close"><i class="fa fa-compress" /></button>
        </t>
    </t>
</templates>