viewpoint vw适配 兼容方案

1、postcss-viewport-units

https://www.npmjs.com/package/postcss-viewport-units

2、viewport-units-buggyfill

https://github.com/rodneyrehm/viewport-units-buggyfill

说明：

postcss-viewport-units主要是给CSS的属性添加content的属性，配合viewport-units-buggyfill库给vw、vh、vmin和vmax做适配的操作。

如：

.box {

    top: 2vw;

    left: 1vw; 

    content: 'viewport-units-buggyfill;top: 2vw;left: 1vw;';

}