Img Class Problem

I am trying to get an image sized through an external stylesheet.  However, when I use the class I built on a page served up by the php shopping cart it seems to ignore the css rules.

I am not able to use my normal tools to see where the conflict might be.  Please help me to get the image to size normally.

img.productlabel {
width:550px;
height:198px;
}

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<img src="/Resources/labels/1606.jpg" class="productlabel" alt="Product Label" />

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You can see an example of the label I am trying to size at
http://www.theherbsplace.com/Vitamin_C_Ascorbates_p_549.html

Please help me to get this to honor the size rules via CSS.

Thanks,

Randal