從CSS實作正片疊底看=>混合模式mix-blend-mode

相容性：這個東西說多了也沒意思，像HTML5和CSS3這種兼容性時刻變化的東東，我們最好在自己支持的設備上實驗，不支持，就在想辦法唄，這個東西就是為了方便好玩

所有屬性：

<span style="color: #800000;">mix-blend-mode: normal;          //正常
mix-blend-mode: multiply;        //正片叠底
mix-blend-mode: screen;          //滤色
mix-blend-mode: overlay;         //叠加
mix-blend-mode: darken;          //变暗
mix-blend-mode: lighten;         //变亮
mix-blend-mode: color-dodge;     //颜色减淡
mix-blend-mode: color-burn;      //颜色加深
mix-blend-mode: hard-light;      //强光
mix-blend-mode: soft-light;      //柔光
mix-blend-mode: difference;      //差值
mix-blend-mode: exclusion;       //排除
mix-blend-mode: hue;             //色相
mix-blend-mode: saturation;      //饱和度
mix-blend-mode: color;           //颜色
mix-blend-mode: luminosity;      //亮度
mix-blend-mode: initial;         //初始
mix-blend-mode: inherit;         //继承
mix-blend-mode: unset;           //复原</span>