Untitled

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<html lang="en">

<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="style.css">
</head>


<script>
        function myFunction() {
            var letters = document.getElementById('text');
            for (var i = 0; i < letters.innerHTML.length; i++) {
                //only change the one you want to
                if (i == 4) {
                    letters.innerHTML = letters.innerHTML.replace(letters[i], '<span style="color: yellow;">'+letters[i]+'</span>');
               }
            }
        }
    </script>

        <div id="text">
            Lorem ipsum dolor sit amet, consectetur adipisicing elit. Fuga, dolores nostrum! Repellendus recusandae eum maiores incidunt
            cum temporibus, exercitationem sequi fugiat, at accusantium, voluptas fuga.
        </div>

    <script>
        myFunction();
    </script>
</html>