ul.list_ok li:before {
  color: rgba(0, 0, 0, 0);
}
ul.list_ok :nth-child(1):before {
  background: url(../imgs/down3-1.png) no-repeat center center;
}
ul.list_ok :nth-child(2):before {
  background: url(../imgs/down3-2.png) no-repeat center center;
}
ul.list_ok :nth-child(3):before {
  background: url(../imgs/down3-3.png) no-repeat center center;
}
.dgroup {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
}
.dgroup img{
  margin: 10px 20px;
}