box.css

.wrapper {
  width: 100%;
}
.pd {
  padding: 1em;
}
.box {
  height: 600px;
  border: 1px solid black;
  box-sizing: border-box;
  float: left;
  margin: 1em;
  position: relative;
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;
  background-color: yellow;
}

.inner {
  background-color: cyan;
  border: 2px solid black;
}
.inner-big {
  margin-top: 1em;
  background-color: cyan;
  border: 2px solid black;
}
.ffb {
  position: absolute;
  left: 0;
}
.fsb {
  position: absolute;
  right: 0;
}
.ftb {
  position: absolute;
  bottom: 1em;
  left: 1em;
}
.sfb {
  width: 44%;
  left: 1em;
  position: absolute;
}
.ssb {
  width: 44%;
  right: 1em;
  position: absolute;
}
.tfb {
  position: absolute;

  left: 1em;
}
.tsb {
  position: absolute;

  right: 1em;
  bottom: 1em;
}
img {
  object-fit: cover;
}
.img1 {
  position: absolute;
  right: 1em;
}
.img2 {
  position: absolute;
  bottom: 1em;
  left: 1em;
}
@media screen and (min-width: 768px) {
  .box {
    width: 30%;
  }
  .inner {
    height: 45%;
  }
  .inner-big {
    height: 90%;
  }
  .sm {
    width: 45%;
  }

  .lg {
    width: 90%;
  }
}

@media screen and (max-width: 768px) {
  .box {
    width: 100%;
  }
  .inner {
    height: 45%;
  }
  .inner-big {
    height: 90%;
  }
  .sm {
    width: 45%;
  }

  .lg {
    width: 90%;
  }
}