.a{
height:500px;
  width:500px;
  border:solid 1px red;
  position: relative;
}
.b{
transform: translate(-50%,-50%);
  position: absolute;
  top: 50%;
  left: 50%;
  display: -webkit-box;
  overflow: hidden;
  text-overflow: ellipsis;
  -webkit-box-orient: vertical;
  -webkit-line-clamp: 3;
}