I need to clear flex box layout item so that first item is 100% width, the second is 50% centered on its own line, and 3rd and 4th are 50% width on the same line.

The clear works normal on simple block items but I can't find a way to do this with flex layout. 

<https://jsfiddle.net/tzx8qyjt/>

```css
.container {
  padding: 0;
  margin: 0;
  list-style: none;
  display: -webkit-box;
  display: -moz-box;
  display: -ms-flexbox;
  display: -webkit-flex;
  display: flex;
  -webkit-flex-flow: row wrap;
  justify-content: space-around;
}

.item {
  background: tomato;
  padding: 5px;
  width: 100%;
  height: 150px;
  margin-top: 10px;
  margin-bottom: 10px;
  line-height: 150px;
  color: white;
  font-weight: bold;
  font-size: 3em;
  text-align: center;
}

.container.block {
  display: block;
}

.container.block .item {
  float: left;
  box-sizing: border-box;
}

.half {
  width: 50%;
}

.container .item.centered {
  float: none;
  clear: both;
  margin-left: auto;
  margin-right: auto;
}
```

```html
<ul class="container">
  <li class="item">1</li>
  <li class="item half centered">2 Clear after me</li>
  <li class="item half">3</li>
  <li class="item half">4</li>
</ul>
<br />
<br />
<br />
<br />
<br />
<ul class="container block">
  <li class="item">1</li>
  <li class="item half centered">2 Clear after me</li>
  <li class="item half">3</li>
  <li class="item half">4</li>
</ul>
```