控制垂直文本流（LTR）始端和末端的边框颜色

实例代码

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>垂直书写模式下的 border-block-color</title>
    <style>
        body {
            font-family: Arial, sans-serif;
            display: flex;
            flex-direction: column;
            align-items: center;
            padding: 20px;
            background-color: #f5f5f5;
        }
        
        h2 {
            color: #333;
            margin-bottom: 30px;
        }
        
        .vertical-example {
            writing-mode: vertical-rl;
            height: 200px;
            width: 150px;
            margin: 20px 0;
            padding: 20px;
            border-block-style: dashed;  /* 边框样式 */
            border-block-width: 8px;     /* 边框宽度 */
            border-block-color: hotpink; /* 边框颜色 */
            background-color: white;
            display: flex;
            align-items: center;
            justify-content: center;
            box-shadow: 0 4px 8px rgba(0,0,0,0.1);
        }
        
        .explanation {
            max-width: 500px;
            background: white;
            padding: 20px;
            border-radius: 8px;
            margin-top: 30px;
            box-shadow: 0 2px 4px rgba(0,0,0,0.1);
        }
        
        .code {
            background: #f0f0f0;
            padding: 10px;
            border-radius: 4px;
            font-family: monospace;
            margin: 10px 0;
        }
        
        .note {
            color: #d63384;
            font-weight: bold;
        }
    </style>
</head>
<body>
    <h2>垂直书写模式下的 border-block-color</h2>
    
    <div class="vertical-example">
        垂直文本方向<br>
        writing-mode: vertical-rl
    </div>
    
    <div class="explanation">
        <h3>代码说明：</h3>
        <div class="code">
            div {
                writing-mode: vertical-rl;
                border-block-style: dashed;
                border-block-width: 8px;
                border-block-color: hotpink;
            }
        </div>
        
        <p><strong>效果解析：</strong></p>
        <ul>
            <li><span class="note">writing-mode: vertical-rl</span> - 设置文本垂直排列，从右到左</li>
            <li>在这种模式下，<span class="note">block方向</span>变为水平方向</li>
            <li><span class="note">border-block-color: hotpink</span> - 应用于block方向的边框颜色</li>
            <li>由于是垂直书写模式，block方向的边框实际上是<span class="note">左右边框</span></li>
            <li>所以你会看到左右两侧有8px宽的粉红色虚线边框</li>
        </ul>
        
        <p><strong>对比说明：</strong></p>
        <p>在默认的水平书写模式下(ltr)，block方向是垂直的(上下边框)，但在垂直书写模式下，block方向变为水平的(左右边框)。</p>
    </div>
</body>
</html>