我想在网格项内部居中对齐内容，水平居中但垂直不居中。在JSfiddle上查看：http://jsfiddle.net/6zs8ydhf/

.container {
  display: grid;
  grid-template-columns: 200px auto;
  grid-template-rows: 400px 200px;
}

.item {
  border: 1px solid #111;
}

.item2 h1 {
  display: flex;
  align-items: center;
  justify-content: center;
}

<div class="container">
  <div class="item item1">
    <h1>1</h1>
  </div>
  <div class="item item2">
    <h1>2 应该居中</h1>
  </div>
  <div class="item item3">
    <h1>3</h1>
  </div>
</div>