为边框图像向外扩展

实例代码

<!DOCTYPE html>
<html>
<head>
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <style>
        body {
            font-family: Arial;
            padding: 20px;
            max-width: 600px;
            margin: 0 auto;
        }
        
        .demo-box {
            width: 200px;
            height: 100px;
            margin: 30px auto;
            background: #f0f8ff;
            border: 20px solid transparent;
            border-image: url('/uploads/20250605/border.png') 30 round;
            display: flex;
            align-items: center;
            justify-content: center;
            position: relative;
        }
        
        .demo-box::after {
            content: "";
            position: absolute;
            top: 0;
            left: 0;
            right: 0;
            bottom: 0;
            border: 1px dashed #999;
        }
        
        .demo-label {
            text-align: center;
            margin-top: 5px;
            font-size: 14px;
            color: #666;
        }
        
        @media (max-width: 480px) {
            .demo-box {
                width: 160px;
                height: 80px;
            }
        }
    </style>
</head>
<body>
    <h2 style="text-align: center;">border-image-outset 6个示例</h2>
    
    <div>
        <div class="demo-box" style="border-image-outset: 0;"></div>
        <div class="demo-label">1. border-image-outset: 0 (默认)</div>
        
        <div class="demo-box" style="border-image-outset: 10px;"></div>
        <div class="demo-label">2. border-image-outset: 10px</div>
        
        <div class="demo-box" style="border-image-outset: 1em 2em;"></div>
        <div class="demo-label">3. border-image-outset: 1em 2em</div>
        
        <div class="demo-box" style="border-image-outset: 10px 20px 30px;"></div>
        <div class="demo-label">4. border-image-outset: 10px 20px 30px</div>
        
        <div class="demo-box" style="border-image-outset: 10px 0 15px 5px;"></div>
        <div class="demo-label">5. border-image-outset: 10px 0 15px 5px</div>
        
        <div class="demo-box" style="border-image-outset: 0.5 1;"></div>
        <div class="demo-label">6. border-image-outset: 0.5 1 (上下0.5倍/左右1倍)</div>
    </div>
</body>
</html>