Change the z-index of "first-col" to -1. That way everything still appears as it is on desktops (since you're using fixed positioning), but the subscription field will gracefully hide to the back when you scroll right on mobile devices.
You might also want to add a background to the article block. Everything in the background (i.e. the subscription field) shows through otherwise.
thanks for that. the mobile view is a mess. i will hotfix your suggestions now.
the site was more a sideproject to get back into coding. i under-estimated the positive response to be honest.