https://developer.mozilla.org/en-US/docs/Web/CSS
https://www.w3schools.com/cssref/css_functions.php
https://tympanus.net/codrops/css_reference/
https://hcdev.ru/css/

https://cssreference.io/

https://github.com/w3c/webref
https://htmlbook.ru/css

https://webref.ru/
http://howtocodeinhtml.com/HowToCodeInHTMLAndCSS.pdf