Hello,

1- Regarding your first concern, kindly please share your Site WP-ADMIN Login details in the Private Content field so that we can check this concern on your Site and help you out accordingly.

2- Please try using the below Custom CSS code and paste it to Dashboard >> Theme Settings >> Custom CSS >> Global CSS section:

.comment-form .submit {
   background: red !important;
   border-color: red !important;
   color: yellow !important;
}

In this CSS, you can change the color to your choice of hex code or color name. Also, the color: yellow property here is for the Text color change if you want to change it. If not just remove this property from the CSS.

Best Regards