body {
  background: #faeee7;
}

.boxes {
  position: relative;
  margin: 200px auto;
  width: 100px;
  height: 100px;
}

.box {
  position: absolute;
  width: 50px;
  height: 50px;
  background: limegreen;
}

/* 左上 */
.box1 {
  top: 0;
  left: 0;
}

/* 右下 */
.box2 {
  bottom: 0;
  right: 0;
}