            <h1 class="heading">Isogram Calculator :</h1>
            <h3 class="about">An isogram is a word in which no letter occurs more than once. </h3>
        </div>
        <div class="input">
            <label for="string">Enter String:</label>
            <input type="text" id="string" required>
        </div>
        <div class="output">
            <button onclick="checkIsogram()">Check</button>
            <div class="output-box">
                <p id="output-text"></p>
            </div>
    