a17.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>

    <style>
        /* li {
            border: 2px solid green;
        } */
        
        div li {
            border: 2px solid green;
        }
    </style>
</head>
<body>
    <!-- Block Level Elements -->

    <div>
        <ol style="border: 2px solid red;">
            <li>a1</li>
            <li>a2</li>
            <li>a3</li>
        </ol>
    </div>

    <ol style="border: 2px solid blue">
        <li>a1</li>
        <li>a2</li>
        <li>a3</li>
    </ol>
</body>
</html>