diff --git a/.changeset/quiet-trainers-dance.md b/.changeset/quiet-trainers-dance.md
new file mode 100644
index 000000000..361050a26
--- /dev/null
+++ b/.changeset/quiet-trainers-dance.md
@@ -0,0 +1,5 @@
+---
+"@primer/primitives": patch
+---
+
+Adding variable for Underlinenav-counter-bg
diff --git a/data/colors/mixins/dark_mode.scss b/data/colors/mixins/dark_mode.scss
index cd785c6da..810d64863 100644
--- a/data/colors/mixins/dark_mode.scss
+++ b/data/colors/mixins/dark_mode.scss
@@ -500,6 +500,7 @@ $export: (
     icon-hover: $gray-1,
     icon-active: $gray-1,
     counter-text: $gray-3,
+    counter-bg: rgba($gray-3, 0.2),
   ),
 
   verified-badge: (
diff --git a/data/colors/mixins/light_mode.scss b/data/colors/mixins/light_mode.scss
index 68aebaf9f..1cdb93d77 100644
--- a/data/colors/mixins/light_mode.scss
+++ b/data/colors/mixins/light_mode.scss
@@ -500,6 +500,7 @@ $export: (
     icon-hover: $gray-4,
     icon-active: $gray-9,
     counter-text: $gray-9,
+    counter-bg: var(--color-counter-bg),
   ),
 
   verified-badge: (