Untitled

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <link rel="stylesheet" href="css/style.css">
</head>
<body>
    <h1 style="display: none;">YOU WIN</h1>
    <h1 style="display: none;">YOU FALSE</h1>
    <div class="nine">
<div class="top">
    <div class="kvad" id="one"></div>
    <div class="kvad" id="two"></div>
    <div class="kvad" id="three"></div>
</div>

<div class="mid">
        <div class="kvad" id="four"></div>
        <div class="kvad" id="five"></div>
        <div class="kvad" id="six"></div>
    </div>
    <div class="bot">
            <div class="kvad" id="seven"></div>
            <div class="kvad" id="eight"></div>
            <div class="kvad" id="nine"></div>
        </div>

    </div>

<h2>ВЫБЕРИТЕ СИМВОЛ</h2>
    <button id="slash" class="slash" onclick = "slash.style.display = 'none', star.style.display = 'none', quest='slash' ">/</button>
    <button id="star" class="star" onclick = "slash.style.display = 'none', star.style.display = 'none', quest='star' ">*</button>


    <script>
    let quest;
    var slash = document.getElementById(slash);
    var star = document.getElementById(star);
    </script>

Uncaught TypeError: Cannot read property 'style' of null at HTMLButtonElement.onclick