[1] https://alistapart.com/article/responsive-web-designSearch in Google Scholar
[2] http://gs.statcounter.com/screen-resolution-stats/all/romania.Search in Google Scholar
[3] Marcotte, E., Responsive Web Design, Second Edition, Publisher: A Book Apart, 2015Search in Google Scholar
[4] http://getbootstrap.com/css/Search in Google Scholar