Double Border on #colspan# Column

I am showing a double border in the column that has #colspan” above. I’ve tried a few things but just can’t seem to get rid of it. Could you please give me the correct coding. This will apply to all my tables.

Example is http://plantbest.info/products/retail/seed/kits/

Many thanks again Tobias!

https://ww.wp.xz.cn/plugins/tablepress/