Adverts_Add page Preview button issue

Hi,
i am not sure if this is the same problem as in the thread you linked to, it seems that in your case the text is just misaligned a bit and maybe too dark, you should be able to fix it by adding the code below in wp-admin / Appearance / Customize / Additional CSS panel

body input[type="submit"].adverts-button {
  color: white !important;
  line-height: 1 !important;
}