<div class="flex-container">
  <div class="flex-item">弹性布局</div>
  <div class="flex-item">弹性布局</div>
  <div class="flex-item">弹性布局</div>
</div>

.flex-container {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 200px;
  background-color: #ccc;
}

.flex-item {
  flex: 1;
  padding: 20px;
  background-color: #f00;
  color: #fff;
  text-align: center;
}