@import url("https://fonts.googleapis.com/css2?family=Source+Sans+Pro:wght@400;600&display=swap");
* {
  margin: 0;
  padding: 0;
}
body {
  font-family: "Source Sans Pro", sans-serif;
  background: aliceblue;
  height: 100vh;
  width: 100vw;
  display: flex;
  justify-content: center;
  align-items: center;
}

.main {
  border: 5px solid grey;
  width: 500px;
  height: 500px;
  background: #ffffff;
  position: relative;
}
.box1 {
  background: teal;
}
.box2 {
  background: orangered;
}
.box3 {
  background: purple;
}

.box {
  height: 100px;
  width: 100px;
  color: white;
  text-align: center;
  line-height: 100px;
}

.box2 {
  position: absolute; /* LTRB */
  right: 0px;
}