这里只是一篇属性参考，详细的教程请参考这篇博客。http://www.ruanyifeng.com/blog/2015/07/flex-grammar.html
flex容器上的属性
flex-direction : row | row-reverse | column | column-reverseflex-wrap: nowrap | wrap | wrap-reverseflex-flow : flex-direction || flex-wrapjustify-content: flex-start | flex-end | center | space-between | space-aroundalign-items : flex-start | flex-end | center | baseline | stretchalign-content : flex-start | flex-end | center | stretch | space-around | stretch
flex项目上的属性
order : integer 越小越靠前flex-grow : number(0) 放大比例flex-shrink : number(1) 缩小比例flex-basis ： length | autoflex : flex-grow || flex-shrink || flex-basisalign-self : auto | flex-start | flex-end | center | baseline | stretch 在这单个flex项目上覆盖flex容器 上设置的align-items属性
