diff --git a/addons/mail/static/src/core/common/core.dark.scss b/addons/mail/static/src/core/common/core.dark.scss
index a261430d7c8..f2f3f5d22de 100644
--- a/addons/mail/static/src/core/common/core.dark.scss
+++ b/addons/mail/static/src/core/common/core.dark.scss
@@ -1,3 +1,3 @@
 .o-discuss-badge {
-    background-color: $primary;
+    --o-discuss-badge-bg: #{$primary}; // sync with --o-navbar-badge-bg
 }
diff --git a/addons/mail/static/src/core/common/core.scss b/addons/mail/static/src/core/common/core.scss
index 863218ac738..05605518b57 100644
--- a/addons/mail/static/src/core/common/core.scss
+++ b/addons/mail/static/src/core/common/core.scss
@@ -10,6 +10,10 @@
     --o-discuss-badge-bg: #{$o-success}; // sync with --o-navbar-badge-bg
     color: $white !important;
     background-color: var(--o-discuss-badge-bg) !important;
+
+    &.o-muted {
+        --o-discuss-badge-bg: #{$gray-400};
+    }
 }
 
 .o-discuss-badge, .o-discuss-badgeShape {
diff --git a/addons/mail/static/src/core/web/discuss_sidebar_mailboxes.xml b/addons/mail/static/src/core/web/discuss_sidebar_mailboxes.xml
index 1649999687e..4a7c9b90173 100644
--- a/addons/mail/static/src/core/web/discuss_sidebar_mailboxes.xml
+++ b/addons/mail/static/src/core/web/discuss_sidebar_mailboxes.xml
@@ -30,7 +30,7 @@
             <span
                 t-if="mailbox.counter > 0"
                 class="o-mail-DiscussSidebar-badge o-discuss-badge badge rounded-pill ms-1 me-3 fw-bold"
-                t-att-class="{ 'bg-400 text-light': mailbox.id === 'starred' }"
+                t-att-class="{ 'o-muted': mailbox.id === 'starred' }"
                 t-esc="mailbox.counter"
             />
         </button>