fireInternet/res/extjs/examples/grid/multiple-sorting.css

.sort-desc {
    background-image: url("../../resources/themes/images/default/grid/sort_desc.gif") !important;
    background-position: 4px 7px !important;
}

.sort-asc {
    background-image: url("../../resources/themes/images/default/grid/sort_asc.gif") !important;
    background-position: 4px 7px !important;
}