Can you try adding this CSS in Appearance > Customize > Additional CSS?:
.comments-area :is(input,textarea) {
border-radius: 5px;
border-color: rgb(207, 207, 207);
color: #464646;
}
.comments-area input[type="submit"]{
background-color: #FF6200;
color: #fff;
}
.comments-area input[type="submit"]:hover{
background-color: #cc4e00;
}
Does that work?