hugo-coder/assets/scss/_notices_dark.scss

@mixin notices_dark {
  .notice {
    .notice-title {
      border-bottom: 1px solid $bg-color-dark;
    }
  }
}

body.colorscheme-dark {
  @include notices_dark();
}

body.colorscheme-auto {
  @media (prefers-color-scheme: dark) {
    @include notices_dark();
  }
}