* {
  box-sizing: border-box;
}

.gallery {
  display: flex;
  list-style: none;
  margin-top: -30px;
  margin-left: -30px;
  padding: 0;
}
.gallery__item {
  flex-basis: calc(100% / 3 - 30px);
  margin-top: 30px;
  margin-left: 30px;
}
.gallery__img {
  display: block;
  width: 100%;
  height: 100%;
}