SG-Double theme remove space before left sidebar

Hi.

Thank for creating such a beautiful Theme.

I have 2 questions

1.
I use the SG-double theme and want to get rid of the space before the left widget and after the right widget. I searched all the CSS files, but cannot find it. When I debug, I see the max. space for the inner part is 1366. If I change it to 1500, then the spaces disappear, so it should be possible. Can you tell me how to do this.

2.
I want to make some more changes and I should be using a child theme, but I am already using the child theme SG-double and I read that is is not possible to make a child theme of another child theme. How should I solve this.

Best regards,
Kees Bond