We have verified. It's working.
Can you read our documentation?
http://www.foxnetsoft.com/t/nopexauthsocial#step12
Please verify scope.
If you will see error again, write to us.
We'll try to help you.
Add this line in top cshtml file.
@using Nop.Web.Framework;
Can you make printscreen?
I opened your site on mobile device (Ipad).
Don't forgot NopCommerce doesn't support mobile themas from version 3.4
I recommend you to copy css from
~/Plugins/FoxNetSoft.Articles/Styles/store1-styles.css
to your main site css file and remove line
Html.AddCssFileParts("~/Plugins/FoxNetSoft.Articles/Styles/store1-styles.css");