前端---css3优化

.front::before {
    content: ‘‘;
    position: fixed; // 代替background-attachment
    width: 100%;
    height: 100%;
    top: 0;
    left: 0;
    background-color: white;
    background: url(/img/front/mm.jpg) no-repeat center center;
    background-size: cover;
    will-change: transform; // 创建新的渲染层
    z-index: -1;
  }