.Grid-HeaderRow {
    color: #000000;
    background-color: #d9edf7; /*lighter*/
    font-family: Tahoma;
    font-size: 12px;
    line-height: 22px;
}

    .Grid-HeaderRow:hover,
    .Grid-HeaderRow:focus {
        color: #000000;
        background-color: #d9edf7; /*lighter*/
        font-family: Tahoma;
        font-size: 12px;
        line-height: 22px;
    }