Now I tried with this code in my custom.css :
form#baform-1 div.ba-form input[type="number"],
form#baform-1 div.ba-form input[type="email"],
form#baform-1 div.ba-form input[type="text"],
form#baform-1 div.ba-form select,
form#baform-1 div.ba-form select[size],
form#baform-1 div.ba-form textarea {
border-color: transparent !important;
border-bottom: 2px solid #6bbb30 !important;
}
And he works great thank.