Change theme style to use code snippet

Hi all,

I just posted this request on the page with the release notes as I had just performed an update, but later realised this is a more suitable place.
I would like to use this code snippet provided by you guys: https://presscustomizr.com/snippet/changing-the-global-column-layout-of-the-customizr-theme/ . However, the snippet works only with the Classical style option, and I can’t find where to set this theme style option. It is not in the advanced options in the Customizer. Any thoughts where to change the theme style so I can use this snippet?
Or, just as well, any other thoughts on how to change the column width of the layout?

Thanks!