UAS2.0_DEV_TEST/app/view/grid/mergeColumn/MergeColumnGrid.scss

.x-merge-grid{
    .x-grid-item-over{
        background-color:#fff !important;
    }
    .x-grid-item{
        border-top-width: 0px !important;
    }
    .x-grid-cell-inner::before{
        border:none !important;
    }
}