Référence en HTML et CSS, site incontournable. Articles clés sur flexbox, box‐sizing, meta responsive, centrer un élément…
https://css-tricks.com

Articles importants :
https://css-tricks.com/lets-look-50-interesting-css-properties-values/
https://css-tricks.com/snippets/css/a-guide-to-flexbox/
https://css-tricks.com/snippets/css/keyframe-animation-syntax/
https://css-tricks.com/inheriting-box-sizing-probably-slightly-better-best-practice/
https://css-tricks.com/snippets/html/responsive-meta-tag/