<!DOCTYPE html>
<html lang="ko">
<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></title>
<link rel="stylesheet" href="main.css" />
</head>
<body>
<div class="alert-box" id="alert">
<p>박스</p>
<button onclick="change('none')">닫기</button>
</div>
<button onclick="change('block','아이디를 입력해주세요')">버튼1</button>
<button onclick="change('block','비밀번호를 입력해주세요')">버튼2</button>
<script>
function change(s1, s2) {
document.getElementById('alert').style.display = s1;
document.getElementById('alert').innerHTML = s2;
}
</script>
</body>
</html>

컴퓨터를 껏다 켜봐도 버튼이 안보이네요... 뭘 잘못 입력했을까요?
그 외는 잘 작동하는데 아무리해도 닫기 버튼이 안보이네요