How do I make table borders invisible in Bigin's Template Editor?

How do I make table borders invisible in Bigin's Template Editor?

Hi, I've imported an HTML template into Bigin. 
Next, I want to add 3 images on the same row, so I'm creating a table with 3 columns et 1 row
The problem is that I can't hide the borders of the table. 
Do you have a tip for this?



I precise that the options on the panel don't work => when I click, nothing happens (EU DC)