form { background-color: aqua; padding: 10px }
form label.control-label { font-size: 18px !important; }

/* All Mobile Sizes (devices and browser) */

@media only screen and (max-width: 767px) {
    h2 { font-size: 30px !important; }
    h3 { font-size: 22px !important; }
    p { font-size: 18px !important; }
   input.btn-app { width: 100%; }
}

@media only screen and (max-width: 320px) {
    h2 { font-size: 23px !important; }
    h3 { font-size: 18px !important; }
    p { font-size: 15px !important; }
   input.btn-app { width: 100%; }
}