<form id="calorieCalculator">
    <label for="gender">Sexo:</label>
    <select id="gender" name="gender">
        <option value="male">Hombre</option>
        <option value="female">Mujer</option>
    </select>
    <br>

    <label for="age">Edad:</label>
    <input type="number" id="age" name="age" min="18" max="76">
    <br>

    <label for="lifestyle">Estilo de vida:</label>
    <select id="lifestyle" name="lifestyle">
        <option value="sedentary">Sedentario</option>
        <option value="moderately_active">Moderadamente activo</option>
        <option value="active">Activo</option>
    </select>
    <br>

    <input type="button" value="Calcular Calorías" onclick="calculateCalories()">
    <br>

    <label for="result">Calorías necesarias:</label>
    <input type="text" id="result" name="result" readonly>
</form>