I am trying to learn about AMP, and there is something I really do not understand. Is it "backward compatible" with desktop HTML? If I create an app, lets say in AngularJS or Rails, and I use only AMP validated html, will my pages still look normal on desktop? Do I need to create a unique front-end specifically for mobile pages, and make those pages AMPed?
Additionally, How do AMP pages interact with CSS, specifically with media queries? I also see that AMP has an inline stylesheet. Can I also have my external "regular" stylesheet?
For AMP pages you cannot use third party JS & CSS. Secondly it works fine for desktop browser as well. But most probably you don't want to do that, because of tag & external resource inclusion limitation. Moreover it will not appear in the google search result on desktop.