css question: Apache Forrest

Hi, I am trying to figure out where I should add some CSS code so that
it will apply to my site.  I have added it to the skinconf.xml with no
apparent luck.  I added the code in <extra-css> and the code is the
following: 

 

img.floatleft {

            float: left

        margin: 10px 10px 0 0 ;

}

 

I then reference it in one of my xml documents as <img class="floatleft"
src="images/notes_Sideview.png">  

 

Does anyone have any idea what to do or where to add the code?  Thanks
so much.  Dana