.mc4wp-form input[type="text"],
.mc4wp-form input[type="email"] {
    font-size: 20px;
}

.mc4wp-form label {
    font-size: 20px;
}

.mc4wp-form input[type="submit"] {
    font-size: 1em; /* or a specific size like 15px */
}

.mc4wp-form .form-intro {
    font-size: 18px;
    font-weight: bold;
    margin-bottom: 15px;
}