如何在弹性项目中垂直居中文本？

div {
  border: 1px solid black;
}

.box {
  display: flex;
  flex-flow: column nowrap;
  justify-content: center;
  align-content: center;
  align-items: stretch;
  height: 200px;
}

.box div {
  order: 1;
  flex: 0 1 auto;
  align-self: auto;
  min-width: 0;
  min-height: auto;
  display: flex;            /* NEW */
  align-items: center;      /* NEW */
}

.box div.C {
  flex: 1 1 auto;
}

  
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