现场演示：我的 HTML 文档

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Example of Alignment of Flex Container's Lines</title>
<style> 
.flex-container {
    width: 500px;
    min-height: 300px;
    margin: 0 auto;
	font-size: 32px;
    border: 1px solid #666;
    /* Safari */
    display: -webkit-flex;
    -webkit-flex-flow: row wrap; /* wrap items to create multi-row flex container */
    -webkit-align-content: space-around;
    /* Standard syntax */
    display: flex;
    flex-flow: row wrap;
    align-content: space-around;
}
.flex-container div {
	width: 150px;
	height: 100px;
}
.red {
    background: #e84d51;
}
.green {;
    background: #7ed636;
}
.blue {
    background: #2f97ff;
}
</style>
</head>
<body>
    <div class="flex-container">
        <div class="red">1</div>
        <div class="green">2</div>
        <div class="blue">3</div>
        <div class="green">4</div>
        <div class="blue">5</div>
        <div class="red">6</div>
    </div>
    <p><strong>Note:</strong> Try the other values for the align-content property like, "flex-start", "flex-end", "center", "space-between" and "stretch" to understand how it aligns the items inside flex container.</p>
</body>
</html>