.portfolio ul.gallery {
  list-style-type: none;
  margin: 0 auto;
  display: flex;
  flex-wrap: wrap;
  padding: 0;
}
.portfolio ul.gallery li {
  flex-basis: 100%;
  padding: 5px;
  max-height: 250px;
}
.portfolio ul.gallery li a {
  display: block;
  margin: 0;
  position: relative;
  overflow: hidden;
  width: 100%;
height: 100%;
}
.portfolio ul.gallery li img.background-img {
  position: inherit;
    display: block;
    max-width: 100%;
    height: 100%;
    width: 100%;
    object-fit: cover;
    object-position: center center;
    transition: all .2s ease;
}
.portfolio ul.gallery li:hover img.background-img {
  -moz-transform: scale(1.1);
    -webkit-transform: scale(1.1);
    transform: scale(1.1);
}
.portfolio ul.gallery li a h3 {
  position: absolute;
  z-index: 2;
  left: 20px;
  bottom: 20px;
  margin: 0;
  color: #fff;
  text-decoration: none;
}
.portfolio ul.gallery li a::before {
  z-index: 1;
  content:'';
  display: block;
  position: absolute;
  width: 100%;
  height: 100%;
  background-color: rgba(0, 0, 0, 0.35);
}
.portfolio ul.gallery li .arrow {
  z-index: 2;
  position: absolute;
  height: auto;
  right: 20px;
  bottom: 20px;
  max-width: 50px;
    max-height: 30px;
}
.portfolio ul.gallery li .arrow img {
  width: 100%;
}
@media only screen and (min-width: 768px) {
  .portfolio ul.gallery li {
    flex-basis: 49%;
    padding: 10px;
      max-height: 300px;
    }

  .portfolio ul.gallery {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    grid-template-rows: auto auto auto;
    max-width: 1420px;
  }
}
@media only screen and (min-width: 1200px) {
  .portfolio ul.gallery {
    grid-template-columns: repeat(3, 1fr);
    grid-template-rows: repeat(5, 1fr);
    max-height: 870px;
  }
  .portfolio ul.gallery li {
  max-height: unset;
  }
  .portfolio ul.gallery li:first-child {
    grid-column: 1;
    grid-row: 1/3;
  }
  .portfolio ul.gallery li:nth-child(2) {
    grid-column: 2;
    grid-row: 1/4;
  }
  .portfolio ul.gallery li:nth-child(3) {
    grid-column: 3;
    grid-row: 1/3;
  }
  .portfolio ul.gallery li:nth-child(4) {
    grid-column: 1;
    grid-row: 3/6;
  }
  .portfolio ul.gallery li:nth-child(5) {
    grid-column: 2;
    grid-row: 4/6;
  }
  .portfolio ul.gallery li:nth-child(6) {
    grid-column: 3;
    grid-row: 3/6;
  }
  .portfolio ul.gallery li a {
    height: 100%;
  }
}