index.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>
    <link rel="stylesheet" href="style.css">
</head>

<body>
    <h1>회원가입</h1>
    <fieldset>
        <label>아이디</label>
        <input type="text" id="username">
        <div class="failure-message hide">아이디는 네 글자 이상이어야 합니다.</div>
        <div class="success-message hide">사용할 수 있는 아이디입니다.</div>
    </fieldset>

    <fieldset>
        <label>비밀번호</label>
        <input type="password">
    </fieldset>

    <fieldset>
        <label>비밀번호 확인</label>
        <input type="password">
    </fieldset>

    <fieldset>
        <button>회원가입</button>
    </fieldset>

    <script src="script.js"></script>
</body>

</html>