Adjust cformsii forms to different platforms

The only way I could find to make my contact form usable on smartphones, is to make it very narrow, by adjusting the width in de plugin-editor. This very narrow look, however, doesn’t look very natural on desktop or tablet. Is there a way to let the form adjust somewhat in width according to the platform? Any help would be very much appreciated. Thanks in Advance.

https://wordpress.org/plugins/cforms2/