注意：background属性中的背景图片和颜色混合，只能在一个background属性中。
属性值：
background-blend-mode: normal; //正常
background-blend-mode: multiply; //正片叠底
background-blend-mode: screen; //滤色
background-blend-mode: overlay; //叠加
background-blend-mode: darken; //变暗
background-blend-mode: lighten; //变亮
background-blend-mode: color-dodge; //颜色减淡
background-blend-mode: color-burn; //颜色加深
background-blend-mode: hard-light; //强光
background-blend-mode: soft-light; //柔光
background-blend-mode: difference; //差值
background-blend-mode: exclusion; //排除
background-blend-mode: hue; //色相
background-blend-mode: saturation; //饱和度
background-blend-mode: color; //颜色
background-blend-mode: luminosity; //亮度
background-blend-mode: initial; //初始
background-blend-mode: inherit; //继承
background-blend-mode: unset; //复原