<style>
    div {
    border: solid green 10px;
    font-size: 60px;
    }
    @media(min-width:800px){ /* 화면 크기가 최소 400px 보다 크다면 실행 */
        div {
            display: none;
        }
    }
</style>

<!doctype html>
<html>
<head>
    <title>WEB1 - html</title>
    <meta charset="utf-8">  

    <style>
        a {
            color: black;
            text-decoration:none;
        }
        h1 {
            font-size: 45px;
            text-align: center;
            border-bottom: 1px solid gray;
            margin: 0;
            padding: 20px;
        }
        #grid ol {
            border-right: 1px solid gray;
            width: 100px;
            margin: 0px;
            padding-left: 33px;
        }

        body{
            margin: 0px;
        }

        #grid {
            display: grid;
            grid-template-columns: 150px 1fr;
        }
        #article {
            padding-left: 25px;
        }   

        @media(max-width:800px){
            #grid {
                display: block;
            }
            #grid ol {
                border-right: none;
            }
        }
    </style>
</head>

<body>
    <h1><a href="index.html">WEB</a></h1>

    <div id="grid">
        <ol>
            <li><a href="1.html">HTML</a></li>
            <li><a href="2.html">CSS</a></li>
            <li><a href="3.html">JavaScript</a></li>
        </ol>
        <div id="article">
            <h2> CSS</h2>
            I'm <u>studying</u> <strong>CSS</strong>.<br>
            Visit <a href="https://www.w3.org/Style/CSS/Overview.en.html">HERE</a> if you want to see the official document of CSS.
            <img src="coding.jpg" width="100%">
        </div>
    </div>
    
</body>
</html>