changing colors

Hi, I would like to change the colors of my multistep donation form.
I’ve added some lines into the style.css of the child theme but they’re not subscribing the default styles ’cause (I guess) the form is into an iframe.

.give-donation-level-btn {
    border-color: #ff8d00 !important;
}
#give-form-9691-1 .give-btn {
    background-color: #ff8d00 !important;
}

I’ve tried both with id and not.
I’ve added the “important” tag but still nothing.
How can I do to change the green of all the elements of my form?
Thank you!

Lia