As DDR menu is based on templates, it depends on the template.
Normally there should be some kind of class in the rendered HTML indicating the active element.
I don;t know if the Accordion  DDR template contains an "active class".

This would be the XSLT to add an active class to a li for a menu:

<li>
                    <xsl:attribute name="class">
                        <xsl:if test="@selected=1"> Active</xsl:if>
                        <xsl:if test="@breadcrumb=1 and @selected!=1"> ActiveParent</xsl:if>

</li>