CSS
- CSS Zen Garden – http://www.csszengarden.com/
- CSS 2.0 specification (W3C) – http://www.w3.org/TR/CSS2/
- CSS Validator – http://jigsaw.w3.org/css-validator/#validate_by_input
- CSS index reference (W3C) – http://www.w3.org/TR/CSS2/indexlist.html
- Selectors (W3C) – http://www.w3.org/TR/CSS2/selector.html
- Declaration block (W3C) – http://www.w3.org/TR/CSS2/syndata.html#rule-sets
- Great article on CSS positioning; In Search of the Holy Grail – http://www.alistapart.com/articles/holygrail
- Designing for pixel density – http://coding.smashingmagazine.com/2012/08/20/towards-retina-web/
- The amazing em unit. An oldie but goodie – http://www.w3.org/WAI/GL/css2em.htm
- CSS3 Cheat Sheet, Nick Schäferhoff – https://websitesetup.org/css3-cheat-sheet/
- A Complete Guide to Flexbox, CSS-tricks – https://css-tricks.com/snippets/css/a-guide-to-flexbox/