table.table thead .sorting {
    background: rgba(0, 0, 0, 0) url("../img/sort_both.png") no-repeat scroll left center;
}

table.table thead .sorting_asc {
    background: rgba(0, 0, 0, 0) url("../img/sort_asc.png") no-repeat scroll left center;
}

table.table thead .sorting_desc {
    background: rgba(0, 0, 0, 0) url("../img/sort_desc.png") no-repeat scroll left center;
}