css/frontend.css
/* Buttons: yellow, theme font, rounded 10px */
#zipredirect input[type=submit],
#zipplus input[type=submit] {
  background-color: #ffd400;
  color: #000;
  border: none;
  border-radius: 10px;
  padding: 10px 16px;
  font-family: inherit;
  font-size: 16px;
  cursor: pointer;
}
#zipredirect input[type="submit"]:hover,
#zipplus input[type="submit"]:hover {
  filter: brightness(0.95);
}

/* Make text inputs inherit theme font too */
#zipredirect input[type="text"],
#zipplus input[type="text"] {
  font-family: inherit;
}