.square {
  width: 500px;
  height: 500px;
}
.rectangle {
  width: 250px;
  height: 50px;
}
.circle {
  border-radius: 50%;
}
.blockRed {
  background-color: red;
}
.blockblue1 {
  background-color: blue;
  display: flex;
  /* 水平居中 */
  justify-content: center;
  /* 垂直置顶（默认就是 flex-start，可以不写） */
  align-items: flex-start;
}
.blockblue2 {
  background-color: blue;
  display: flex;
  justify-content: center; /* 水平居中 */
  align-items: flex-end; /* 垂直置底 */
}
.container {
  display: flex;
}