If you created a website using kadence free or pro theme, and want to change style of the comment form fields then in Kadence theme settings there is no option available to manage that. You have to add a custom css code to change the style of the comment form.

You can do that by adding following code inside the theme customizer from

Appearance => Customize => Additional CSS

/* Change Label Colors */
label.float-label {
    color: blue !important;

/* Change Placeholder Colors */
#comment::placeholder, #author::placeholder, #email::placeholder, #url::placeholder {
     color: red !important;

/* Change The Background Colors and text color */
#comments input[type=text], #comments input[type=url], #comments input[type=email], textarea#comment {
     background-color: white;

Change colors according to your requirements.