<html>
<head>
<style>
div#main
{
width:220px;
height:300px;
border:1px solid black;
display:flex;
align-items:center;
}
div#main div
{
flex: 1;
}
</style>
</head>
<body>
<div id="main">
<div style="background-color:coral;">红色</div>
<div style="background-color:lightblue;">蓝色</div>
<div style="background-color:lightgreen;">带有更多内容的绿色 div</div>
</div>
<p>点击“尝试一下”按钮，设置 alignItems 属性的值为 "flex-start"。</p>
<button onclick="myFunction()">尝试一下</button>
<script>
function myFunction()
{
document.getElementById("main").style.alignItems = "flex-start";
}
</script>
<p><b>注意：</b>Safari 不支持 alignItems 属性。</p>
</body>
</html>