https://www.webopedia.com/definitions/responsive-web-design/ 
https://codepen.io/nickpettit/pen/AyaGb
https://www.youtube.com/ 
https://blog.prototypr.io/8-rules-for-perfect-typography-in-ui-21b37f6f23ce
https://www.hongkiat.com/blog/css-viewport-units-vw-vh-wmin-vmax/
https://www.mydevice.io/
https://caniuse.com/ 
https://gs.statcounter.com/screen-resolution-stats
https://www.w3.org/TR/mediaqueries-4/
http://tutorials.jenkov.com/css/media-queries.html
https://webplatform.github.io/docs/tutorials/media_queries/
https://developer.mozilla.org/en-US/docs/Web/CSS/Media_Queries/Using_media_queries 
https://developer.mozilla.org/en-US/docs/Web/CSS/Media_Queries/Using_media_queries#Negating_a_feature_with_not
https://developer.mozilla.org/en-US/docs/tag/Media%20Queries
https://www.w3schools.com/css/css3_mediaqueries_ex.asp
<picture> element  https://www.w3schools.com/tags/tryit.asp?filename=tryhtml5_picture
<video> elements   https://www.w3schools.com/html/html5_video.asp
https://getbootstrap.com/
https://foundation.zurb.com/
https://semantic-ui.com/
https://www.w3schools.com/w3css/

