mobile view : http://mobiletest.me/htc_one_emulator/?u=https://bike2change.de/testing-individual-css-and-div
css boxoxes:
https://www.on-design.de/tutor/html5_css3/css3/flexbox.html
boxlayout examples: https://xhtmlforum.de/71919-drei-responsive-boxen-divs-zentriert-nebeneinander.html
https://www.w3schools.com/Css/css_float.asp
css border: https://www.w3schools.com/css/css_border.asp
