customizing QTabWidget

I want to cancel the underline (only the selected tab's underline) when the tab was selected.

QTabWidget::pane { /* The tab widget frame */
        border-top: 1px solid #C2C7CB;  /* here is the line*/
     padding:20px;
    }        
    QTabWidget::tab-bar {
        left: 2px; /* move to the right by 5px */           
    }
    QTabWidget{
        background-color:#ffffff;
    }
    /* Style the tab using the tab sub-control. Note that
        it reads QTabBar _not_ QTabWidget */
    QTabBar::tab {
        margin-left:4px;
        padding:4px;
        border-top-left-radius: 6px;
        border-top-right-radius: 6px;
        background:#ffffff;
        border:1px solid #d9d9d9;
        border-bottom:0px none;
        min-height:20px;
    }
    QTabBar::tab:selected {
        border-color: #9B9B9B;
        border-bottom-color: #00ffff; /* same as pane color */
        margin-bottom:-1px;    
                                             
    }

here when the tab is selected, I want the tab to lower one px. so as to cover the line. but the line is in front of the tab What can I do to fix it? thank you very much.