1.HTML5 + CSS3  http://learn.shayhowe.com/html-css/
2.BEM: https://en.bem.info/methodology/        
       Focus on:
               - Key Concepts
               - Naming Convention
3.SMACSS: https://smacss.com/
4.SASS: http://sass-lang.com/
5.Javascript(ES5) : http://eloquentjavascript.net/
6.