How can i change button Hover Color?

Put this CSS code in Dashboard > Comments > Settings > Styling > Custom CSS Textarea. Save it, delete all caches and do Ctrl+F5 on front-end.

#wpcomm input[type="submit"]:hover{
border: 1px solid #DD0000 !important;;
background-color: #DD0000 !important;;
}

Don't forget to change the red marked color codes before using.