Cross tab - Design studio - CSS in high contrast black thema : bottom line still visible

Hello Experts,

My requirement is to hide the border lines in a cross tab.

I have used CSS class and made the borders invisible. Thema used : High contrast black.

However one bottom line keeps appearing and I am not able to hide this line. I am sure this is not border line.

Please have a look at the image.

Any ideas.

Thanks.