css设置样式宽度

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CSS Width Example</title>
    <style>
        .container {
            width: 80%; /* 相对宽度 */
            margin: 0 auto;
            border: 1px solid black;
        }
        .box {
            width: 200px; /* 固定宽度 */
            height: 100px;
            background-color: blue;
            margin: 10px;
        }
        .flex-box {
            width: 100%; /* 自动宽度 */
            display: flex;
        }
        .flex-item {
            width: 33.33%; /* 相对宽度 */
            height: 100px;
            background-color: red;
        }
    </style>
</head>
<body>
    <div class="container">
        <div class="box"></div>
        <div class="flex-box">
            <div class="flex-item"></div>
            <div class="flex-item"></div>
            <div class="flex-item"></div>
        </div>
    </div>
</body>
</html>

@media (max-width: 600px) {
    .container {
        width: 100%;
    }
}