https://code.tutsplus.com/tutorials/the-30-css-selectors-you-must-memorize--net-16048
https://css-tricks.com/almanac/selectors/
https://en.wikipedia.org/wiki/Comparison_of_browser_engines_(CSS_support)
https://css-tricks.com/reboot-resets-reasoning/
https://github.com/necolas/normalize.css/
https://www.hostinger.in/tutorials/difference-between-inline-external-and-internal-css
https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Box_Model/Introduction_to_the_CSS_box_model
https://gist.github.com/dcneiner/1137601
https://css-tricks.com/specifics-on-css-specificity/
https://specificity.keegan.st/
https://developer.mozilla.org/en-US/docs/Web/CSS/Specificity
https://developer.mozilla.org/en-US/docs/Learn/CSS/Building_blocks/Selectors/Pseudo-classes_and_pseudo-elements \
https://bitsofco.de/initial-inherit-unset-and-revert/ \
https://www.digitalocean.com/community/tutorials/css-css-units-explained \