<html>
    <table style="width:100%; background-color:red"><tr><td>

        <table style="background-color:blue"><tr><td>

            <table style="width:50%; background-color:green; table-layout:fixed"><tr><td>
                Content
            </td></tr></table>

        </td></tr></table>

    </td></tr></table>
</html>