#container {
    display: flex;
    justify-content: space-between;
    background-color: lightgrey;
}

#container > div {
  height: 100px;
  border: 2px dashed red;
  
  /*This is only for looks*/
  text-align: center;
  padding: 5px;
}

<div id="container">
  <div>Left Side</div>
  <div>I want this centered</div>
  <div>Right Side (Extra text for extra length)</div>
</div>

解决方法@H_301_8@

您可以使用边距来近似居中.但是为了在各种视口中保持一致的flexBox完美居中,你必须稍微修改一下你的HTML.

您需要使用display：inline-flex声明将#container的直接子项转换为flex容器,并为它们赋予flex值1和justify-content：center.

从那里,您将您的内容添加到子div.要在左右div上对齐,请分别使用margin-right：auto和margin-left：auto.

#container {
  display: flex;
  background-color: lightgrey;
}
.flex {
  flex: 1;
  display: inline-flex;
  justify-content: center;
}
.flex > div {
  height: 100px;
  border: 2px dashed red;
  text-align: center;
  padding: 5px;
}
.left div {
  margin-right: auto;
}
.right div {
  margin-left: auto;
}

<div id="container">
  <div class="left flex">
    <div>Left Side</div>
  </div>
  <div class="center flex">
    <div>I want this centered</div>
  </div>
  <div class="right flex">
    <div>Right Side (Extra text for extra length)</div>
  </div>
</div>