.swiper {
  width: 600px;
  height: 400px;
}

@media screen and (max-width: 768px) {
  .swiper {
    width: 400px;
    height: 300px;
  }
}

.first_slide {
  background-color: red;
  color: white;
}

.second_slide {
  background-color: blue;
  color: white;
}

.third_slide {
  background-color: green;
  color: white;
}