changing font-size of caption

Hello,

after managing to align the caption of a figure to left, I know want to  
reduce the font size, maybe change the font itself. How would I do that?

For left-aligning I've already included
   <xsl:template match="caption">
     <fo:block>
       <xsl:attribute name="text-align">
         <xsl:choose>
           <xsl:when test="@align != ''">
             <xsl:value-of select="@align"/>
           </xsl:when>
           <xsl:otherwise>left</xsl:otherwise>
         </xsl:choose>
       </xsl:attribute>
       <xsl:apply-templates/>
     </fo:block>
   </xsl:template>

in my customization-layer.

best regards
Steffen