Problem with change aligned form to stacked

With pure purecss (pure.css) aligned form changes itself into stacked form on mobile or small screen. If I use generated css from skinbuilder (skin.css) then this feature doesn't work anymore.

I tried replace pure.css, load pure.css before skin.css and load pure.css after skin.css. Nothing works. (I hope that right way is to replace pure.css, isn't it?)
