html - flex 元素不垂直居中

Question

我尝试使用 flexbox 将内容垂直居中，但没有成功。我不喜欢使用 position 或 translate 因为它不是固定大小。我的代码有什么问题？

.row-centered {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    align-items: center;
}

.col-centered {
    display: flex;
    flex-direction: column;
    align-self: flex-start;
    float: none;
    margin-right: 0 auto;
}

.us-container{
  display: flex;
  justify-content: center;
  align-items: center;
  vertical-align: middle;
  resize: both;
  overflow: auto;
}

.us-container div{
  resize: both;
  overflow: auto;
}

    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">

<section id="us" class="container-fluid">
        <div class="row row-centered  us-container">
            <div class="col-sm-8 col-md-8 col-xs-8 col-centered ">
                <p class="text-justify">blah blah blah blah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blah </p>
                <h3 class="text-center">blah blah blah</h3>
            </div>
            </div>
    </section>

Answer 1

你的 flex 容器没有额外的高度。唯一的高度是内容的高度。因此，没有垂直居中的空间。

第一步，增加一些高度:

.row-centered {  
  display: flex;
  height: 100vh;
}

第二步，删除不必要的规则，其中一些规则会阻止垂直对齐。

.col-centered {
    display: flex;
    flex-direction: column;
   /* align-self: flex-start;
    float: none;
    margin-right: 0 auto; */
}

.row-centered {
  display: flex;
  height: 100vh;
}
.col-centered {
  display: flex;
  flex-direction: column;
}
.us-container {
  display: flex;
  justify-content: center;
  align-items: center;

}

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet" />
<section id="us" class="container-fluid">
  <div class="row row-centered us-container">
    <div class="col-sm-8 col-md-8 col-xs-8 col-centered ">
      <p class="text-justify">blah blah blah blah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah
        blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blahblah blah blah</p>
      <h3 class="text-center">blah blah blah</h3>
    </div>
  </div>
</section>