Restrict Page login responsive page

We are working on a site using a responsive them (Consulting v3.4 from StylemixThemes) and child theme on WordPress 4.7 using Page Restrict v2.2.6. We expect half of our traffic to be traditional desktop and the other to be mobile devices. Currently the login is left justified so it works for both but we would love it if the Page Restrict login was able to be centered in an active class that is sized to 100% of the viewport so the presentation works correctly for both desktop and mobile. On our internal development site we centered the class but when viewed on a mobile device the login fields are off the page.