How to remove grey border in Sider theme from Site Library

Hi,

I'm using GeneratePress premium with Elementor Pro. I need to design a site that uses Vertical Navigation and so I thought a good starting point would be to install your Sider theme from Site Library. Whilst I like the look of this theme I notice that the right hand side where the content lives has a grey border. Ideally I don't want a border and prefer that whatever I create in Elementor takes up the whole of the right hand pane.

How can I achieve this?

Thanks
Gary