How to modify the input checkbox CSS?

I'm currently helping a friend putting up a website (you can see it here : https://debrouille-bandit.fr/), and I can't figure how to change the CSS of the input checkbox in the newsletter form. I've tried a lot and you can see that my last attempt is actually shown in the inspector but not on page and I don't know why.

Current CSS rules are :

input[type="checkbox" i] {
  background-color: orange !important;
    color: #ffffff !important;}

i'd like to also change the CSS of the focus action.

Thanks a lot for your time !