body {
  display: flex;
  flex-direction: column;
}

ul {
  list-style: none;
  max-width: 1200px;
  margin: 0 auto;
}
ul li {
  float: left;
  width: 16.666%;
  height: 600px;
  opacity: 0.5;
  -moz-transition: all 0.5s ease-in-out;
  -ms-transition: all 0.5s ease-in-out;
  -webkit-transition: all 0.5s ease-in-out;
  transition: all 0.5s ease-in-out;
}
ul li:hover, ul li:first-child ~ li:last-child {
  width: 50%;
  opacity: 1;
  -moz-transition: all 0.5s ease-in-out;
  -ms-transition: all 0.5s ease-in-out;
  -webkit-transition: all 0.5s ease-in-out;
  transition: all 0.5s ease-in-out;
}
ul li:hover ~ li:last-child {
  width: 16.666%;
  opacity: 0.4;
}
ul li:nth-child(1) {
  background: url("https://uusitaloarja.fi/wp-content/uploads/2021/05/Nuuksio-Petteri.jpg") top center no-repeat;
}
ul li:nth-child(2) {
  background: url("https://uusitaloarja.fi/wp-content/uploads/2021/05/Nuuksio-palaveri.jpg") top right no-repeat;
}
ul li:nth-child(3) {
  background: url("https://uusitaloarja.fi/wp-content/uploads/2021/05/Nuuksio-Group.jpg") top center no-repeat;
}
ul li:nth-child(4) {
  background: url("https://uusitaloarja.fi/wp-content/uploads/2021/05/Nuuksio-Arja.jpg") top center no-repeat;
}

/** Add cool filter effects **/
ul li::before {
  content: "";
  display: block;
  width: 0;
  height: 100%;
  -moz-transition: all 0.5s ease-in-out;
  -ms-transition: all 0.5s ease-in-out;
  -webkit-transition: all 0.5s ease-in-out;
  transition: all 0.5s ease-in-out;
}

@media only screen and (max-width: 480px) {
  ul {
      margin-left: -50px;
      margin-right: -10px;   
  }
}