Ah ok I see what you want now
What you would need to do is rub the line out using the bottom border of the active tab.
Usually you would have the tabs sitting on the border so that the border bottom of the tab and the border-top of the div are in the same place. You can do this by shifting all the tabs down 1px with relative positioning.
On hover you just change the background colour of the active tab and the border-bottom color to match the background of the div below and thus rub out the border. The tabs on top should have a higher z-index than the element below so that it stays on top.
Or you can add 1px padding-bottom on hover and remove the bottom border at the same time as in this example.
You haven't provided enough code for me to apply it to your code properly.