body {
    font-family: 'Arial', sans-serif;
    background-color: #f9f9f9;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: flex-start;
    min-height: 100vh;
    margin: 0;
    padding: 20px;
}

/* Encabezado */
h1 {
    color: #2c3e50;
    margin-bottom: 30px;
}

/* Fieldset y formulario */
fieldset {
    border: 2px solid #3498db;
    border-radius: 10px;
    padding: 20px;
    max-width: 300px;
    width: 100%;
    background-color: #fff;
}

legend {
    font-weight: bold;
    color: #3498db;
    font-size: 18px;
}

/* Inputs */
input[type="number"] {
    width: 100%;
    padding: 10px;
    margin: 10px 0;
    border: 1px solid #ccc;
    border-radius: 5px;
    font-size: 16px;
}

input[type="submit"] {
    width: 100%;
    padding: 10px;
    background-color: #3498db;
    color: white;
    border: none;
    border-radius: 5px;
    font-size: 16px;
    cursor: pointer;
    transition: background-color 0.3s ease;
}

input[type="submit"]:hover {
    background-color: #2980b9;
}

/* Mensaje del resultado */
.resultado {
    margin-top: 20px;
    font-size: 18px;
    color: #e74c3c;
    font-weight: bold;
}