*{
  margin: 0px;
  padding: 0px;
}
body{min-width:1170px;}
.big{
  height: 332px;
  margin:auto;
  position: relative;/*参照物*/
}
.pic{
  width: 100%;
  height: 100%;
}
.pic img{
  position: absolute;/*绝对定位*/
  display: none;
  width: 100%;
  height: 100%;
}
.arr{
  width: 40px;
  height: 70px;
  font-size: 30px;
  font-weight: 900;
  line-height: 70px;
  text-align: center;
  color: #ccc;
  position: absolute;
  top: 125px;
  display: none;
  cursor: pointer;
}
.l-arr{
  left: 0px;
}
.r-arr{
  right: 0px;
}
.big:hover .arr{
  display: block;
}
.arr:hover{
  background: rgba(0,0,0,0.3);
  color: #fff;
}
.but{
  position: absolute;
  bottom: 15px;
  right: 12px;
}