<div class="container">
  <div class="center">center</div>
  <div class="left">left</div>
  <div class="right">right</div>
</div>
.container {
    display: flex;
}

.center {
  flex-grow: 1;   /* flex: 1; 也行 */
  height: 150px;
  background-color: #94e8ff;
}

.left {
  order: -1;
  width: 100px;
  height: 150px;
  background-color: #ffb5bf;
}
.right {
  width: 200px;
  height: 150px;
  background-color: #8990d5;
}

External CSS

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External JavaScript

This Pen doesn't use any external JavaScript resources.