.slick-slide a.img1 {
  background-image: url(../img/slide/1.jpg);
}
.slick-slide a.img2 {
  background-image: url(../img/slide/2.jpg);
}
.slick-slide a.img3 {
  background-image: url(../img/slide/3.jpg);
}
.slick-slide a.img4 {
  background-image: url(../img/slide/4.jpg);
}