on my site I want the form to fill the screen on mobile phones [on hold]

I tried setting max-width:95% on my form for screen with max-width:760px, but something is overriding it, maybe because it doesn't see my device as smaller than 760px? Or because the max-width:600px overrides the max-width:95% due to pixels overriding %?

I am also open to any suggestions on getting the sizing right overall as I am not used to making mobile-friendly sites from the ground up, usually I just take a responsive template >.<

Thanks!