.container div {
  /* width: 100px;
  inline-size: 100px; */
  height: 100px;
  block-size: 100px;
  text-align: center;
  line-height: 100px;
}
.container {
  border: 10px solid currentColor;
  /* flow-root를 쓰면 부모가 박스 4까지 모두 포함함  */
  display: flow-root;

  /* bfc 트릭을 가져다 쓴 것 */
  /* overflow: hidden; */
}
div.box1 {
  background-color: sandybrown;
  float: left;
  width: 100px;
  inline-size: 100px;
}
div.box2 {
  background-color: skyblue;
  height: auto;
  block-size: auto;
  line-height: 1;
  text-align: left;
}
div.box3 {
  background-color: lightgreen;
  clear: both;
  margin-top: 20px;
  margin-block-start: 20px;
  width: 200px;
  inline-size: 200px;
  float: right;
}
div.box4 {
  background-color: yellow;
  width: 300px;
  inline-size: 300px;
  >sni
}