1.1.1. 2.1.3 鼠标悬停显示遮罩层-提高

sass 文件

.box99 {  
  /*外层相对位置*/  
  position: relative;  
  .course-img {  
    /*定位*/  
  position: absolute;  
  z-index: 1;  
  img {  
      /*定形*/  
  width: 220px;  
  height: 160px;  
  }  
  }  
  .title {  
    /*定位*/  
  position: absolute;  
  z-index: 3;  
  /*定形*/  
  width: 220px;  
  h3 {  
      margin-top: 125px;  
  font-size: 15px;  
  color: #333;  
  line-height: 40px;  
  padding-left: 10px;  
  letter-spacing: 1px;  
  }  
  }  
  .title-cover {  
    /*定位*/  
  position: absolute;  
  z-index: 2;  
  margin-top: 125px;  
  /*定形*/  
  width: 220px;  
  height: 35px;  
  /*样式*/  
  background-color: rgba(225, 225, 225, 0.8);  
  }  
  .block {  
    /*定位*/  
  position: absolute;  
  z-index: 2;  
  margin-top: 160px;  
  /*定形*/  
  height: 70px;  
  width: 220px;  
  /*样式*/  
  padding: 6px 10px;  
  border-top: 1px solid #DEDEDE; /*分割线*/  
  background-color: #f9f9fa;  
  .time {  
      font-size: 13px;  
  }  
    .bar {  
      /*样式*/  
  overflow: hidden;  
  background-color: #ccc;  
  height: 4px;  
  width: auto;  
  margin: 13px 0 5px;  
  border-radius: 4px;  
  .percent {  
        width: 40%;  
  height: 4px;  
  background-color: #1ECD97;  
  }  
    }  
    .task {  
      font-size: 13px;  
  }  
  }  
  a {  
    .start {  
      /*定位*/  
  position: absolute;  
  z-index: 5;  
  top: 0;  
  /*定形*/  
  width: 220px;  
  height: 230px;  
  /*样式*/  
  opacity: 0; /*隐藏*/  
  background: rgba(101, 101, 101, 0.6);  
  color: #fff;  
  text-align: center;  
  padding-top: 80px;  
  }  
    &:hover {  
      .start {  
        opacity: 1;/*显示*/  
  }  
    }  
  }  
}

html 文件

<div class="box99">  
  <div class="course-img">  
    <%=  image_tag("https://ws3.sinaimg.cn/large/006tNbRwgy1fvziqfqj28j30et08c74m.jpg") %>  
  </div>  
  <div class="title">  
    <h3>百宝箱</h3>  
  </div>  
  <div class="title-cover"></div>  
  <div class="block">  
    <p class="time">预计学习时间： 7小时</p>  
    <div class="bar">  
      <div class="percent"></div>  
    </div>  
    <p class="task">共1个作业，已完成0个</p>  
  </div>  
  <a href="#">  
    <div class="start">  
      <button type="button" class="btn btn-success">进入课程</button>  
    </div>  
  </a>  
</div>