body, .wrapper, #slider, .image, .vertical-align-wrapper {
  width: 100%;
  height: 100vh;
}

.wrapper { position: relative; }

.arrow {
  cursor: pointer;
  position: absolute;
  width: 0;
  height: 0;
  border-style: solid;
  top: 50%;
  margin-top: -50px;
}

#left-arrow {
  border-width: 50px 40px 50px 0;
  border-color: transparent #ffffff transparent transparent;
  left: 0;
  margin-left: 25px;
}

#right-arrow {
  border-width: 50px 0 50px 40px;
  border-color: transparent transparent transparent #ffffff;
  right: 0;
  margin-right: 25px;
}

.image {
  background-size: cover;
  background-position: center;
  background-repeat: no-repeat;
}

.vertical-align-wrapper {
  display: table;
  overflow: hidden;
  text-align: center;
}

.vertical-align-wrapper span {
  display: table-cell;
  vertical-align: middle;
  font-size: 5rem;
  color: #ffffff;
}

.image-one { background-image: url("https://unsplash.it/1920/1080?image=874"); }

.image-two { background-image: url("https://unsplash.it/1920/1080?image=863"); }

.image-three { background-image: url("https://unsplash.it/1920/1080?image=868"); }
 @media only screen and (max-width : 992px) {

.vertical-align-wrapper span { font-size: 2.5rem; }

#left-arrow {
  border-width: 30px 20px 30px 0;
  margin-left: 15px;
}

#right-arrow {
  border-width: 30px 0 30px 20px;
  margin-right: 15px;
}

.arrow { margin-top: -30px; }
}