JSFiddle - React, Tailwind, and code Playground

HTML

<html>
<head>
<title>Kostka losujaca oceny z matmy.</title>
<link rel="stylesheet" type="text/css" href="style2.css" />
 
</head>

<script>
    function losuj(){
        var zmienna = Math.floor(Math.random() * 6+1);
        
        console.log(zmienna)
        //window.alert('brak wartości');
        //document.write('zła wartość');
        document.forml.losowa.value = zmienna;
        document.getElementById('img').src = 'https://cdn3.iconfinder.com/data/icons/letters-and-numbers-1/32/number_' + zmienna + '_green-128.png';
    }
</script>

<body>
    <h1>Kostka do gry</h1>
    
        <img src="https://cdn3.iconfinder.com/data/icons/letters-and-numbers-1/32/number_1_green-128.png" alt="Image" id="img" />
            
        <form name="forml">
        <input type="button" value="losuj" onclick="losuj()" />
        <input type="text" size="5" name="losowa" />
        </form>
    </body>
</html>