.o_web_client:where(:has(.o-mail-Discuss)) {
    --mail-Discuss-surface-dark: #{mix($white, $o-webclient-background-color, 15%)};
    --NavBar-entry-backgroundColor: var(--mail-Discuss-surface-dark);

    .o_main_navbar, .o_control_panel, .breadcrumb {
        background-color: var(--mail-Discuss-surface-dark);
    }
    .breadcrumb .btn-light {
        --btn-bg: var(--mail-Discuss-surface-dark);
        border-color: transparent;
    }
}