代码示例：（标识：css3_flexbox_align-items_stretch）
<!DOCTYPE html>
<html>
<head>
<style>
.flex-container {
display: flex;
height: 200px;
align-items: stretch;
background-color: DodgerBlue;
}
.flex-container > div {
background-color: #f1f1f1;
width: 100px;
margin: 10px;
text-align: center;
line-height: 75px;
font-size: 30px;
}
</style>
</head>
<body>
<h1>align-items 属性</h1>
<p>"align-items: stretch;" 拉伸 flex 项目以填充容器（默认）：</p>
<div class="flex-container">
<div>1</div>
<div>2</div>
<div>3</div>
</div>
</body>
</html>
