css div边框动态移动

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CSS 动态边框示例</title>
    <style>
        .box {
            width: 100px;
            height: 100px;
            background-color: lightblue;
            border: 2px solid black;
            animation: moveBorder 2s infinite alternate;
        }

        @keyframes moveBorder {
            from {
                border-left-color: red;
            }
            to {
                border-left-color: blue;
            }
        }
    </style>
</head>
<body>
    <div class="box"></div>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>JavaScript 动态边框示例</title>
    <style>
        .box {
            width: 100px;
            height: 100px;
            background-color: lightblue;
            border: 2px solid black;
        }
    </style>
</head>
<body>
    <div class="box" id="box"></div>
    <script>
        const box = document.getElementById('box');
        let direction = 1;
        setInterval(() => {
            const currentColor = box.style.borderColor;
            const colors = currentColor.split(',');
            colors[3] = (parseInt(colors[3].slice(0, -2)) + direction).toString() + 'px';
            box.style.borderColor = colors.join(',');
            direction *= -1;
        }, 100);
    </script>
</body>
</html>