Recapcha set required

index.js

window.onload = function() {
    var $recaptcha = document.querySelector('#g-recaptcha-response');

    if($recaptcha) {
        $recaptcha.setAttribute("required", "required");
    }
};

style.css

#g-recaptcha-response {
    display: block !important;
    position: absolute;
    margin: -78px 0 0 0 !important;
    width: 302px !important;
    height: 76px !important;
    z-index: -999999;
    opacity: 0;
}