Google visualisation table, how to remove default twin-tone th image using css?

Please refer to the following link: http://code.google.com/p/browserscope/source/browse/trunk/static/goog_table.css?r=765

.开发者_Python百科google-visualization-table-tr-head, .google-visualization-table-tr-head td, .google-visualization-table-tr-head-nonstrict 
{    
    font-weight: bold;    
    background: #fff url(//ajax.googleapis.com/ajax/static/modules/gviz/1.0/table/title-bg.gif) repeat-x left bottom;    
    text-align: center;  
} 

I am trying to remove the default table header image, which would appear to be the above gif. I replace that line with, just for testing, background-color:xxx; and nothing seems to get rid of the default image?

Can anyone help?

Have you tried setting background-image:none !important; ?