Workaround: Use the following styles

html .RadGrid_Windows7 .rgSave,
html .RadGrid_Windows7 .rgAdd,
html .RadGrid_Windows7 .rgRefresh,
html .RadGrid_Windows7 .rgEdit,
html .RadGrid_Windows7 .rgDel,
html .RadGrid_Windows7 .rgFilter,
html .RadGrid_Windows7 .rgPagePrev,
html .RadGrid_Windows7 .rgPageNext,
html .RadGrid_Windows7 .rgPageFirst,
html .RadGrid_Windows7 .rgPageLast,
html .RadGrid_Windows7 .rgExpand,
html .RadGrid_Windows7 .rgCollapse,
html .RadGrid_Windows7 .rgSortAsc,
html .RadGrid_Windows7 .rgSortDesc,
html .RadGrid_Windows7 .rgUpdate,
html .RadGrid_Windows7 .rgCancel,
html .RadGrid_Windows7 .rgUngroup,
html .RadGrid_Windows7 .rgExpXLS,
html .RadGrid_Windows7 .rgExpDOC,
html .RadGrid_Windows7 .rgExpPDF,
html .RadGrid_Windows7 .rgExpCSV {
    background-image: none;
}

html .RadGrid_Windows7 th.rgSorted {
        background-image: none;
}

html .RadGrid_Windows7 .rgMasterTable .rgSelectedCell,
html .RadGrid_Windows7 .rgSelectedRow {
        background-image: none;
}

html .RadGrid_Windows7 .rgMasterTable .rgActiveCell,
html .RadGrid_Windows7 .rgActiveRow,
html .RadGrid_Windows7 .rgHoveredRow {
           
        background-image: none;
}

html .RadGrid_Windows7 .rgEditRow {
        background-image: none;
}

html .RadGrid_Windows7 .rgPager {
    background-image: none;
}

    html .RadGrid_Windows7 .rgPager .rgPagerButton {
            background-image: none;
    }

html .RadGrid_Windows7 .rgNumPart a:hover,
html .RadGrid_Windows7 .rgNumPart a.rgCurrentPage {
        background-image: none;
}

    html .RadGrid_Windows7 .rgNumPart a:hover span,
    html .RadGrid_Windows7 .rgNumPart a.rgCurrentPage span {
            background-image: none;
    }

html .GridReorderTop_Windows7 {
    background-image: none;
}

html .GridReorderBottom_Windows7 {
    background-image: none;
}

html .RadGrid_Windows7 .rgGroupPanel {
    background-image: none;
}

html .RadGrid_Windows7 .rgGroupItem {
        background-image: none;
}

html .RadGrid_Windows7 .rgGroupHeader {
    background-image: none;
}

html .RadGrid_Windows7 .rgCommandRow {
    background-image: none;
}