This is a great introduction to responsive webdesign:

• Video https://www.youtube.com/watch?v=T-hVjfc7E-c
• Slides https://docs.google.com/presentation/d/1uG20FaNBMQGNjMZGN1SelJ05HVBm5u6fRSCj5ldFftg/edit
• Excercise https://developers.google.com/web/ilt/pwa/lab-responsive-design