diff --git a/package-lock.json b/package-lock.json
index c0e984e1b80d..e6a132aef668 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -10,7 +10,7 @@
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         "@hapi/accept": "^5.0.2",
         "@primer/components": "^30.3.0",
-        "@primer/css": "^17.9.0",
+        "@primer/css": "^21.5.1",
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@@ -3629,6 +3629,21 @@
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+      "resolved": "https://registry.npmjs.org/@prettier/sync/-/sync-0.5.2.tgz",
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+      },
+      "funding": {
+        "url": "https://github.com/prettier/prettier-synchronized?sponsor=1"
+      },
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+      }
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       "resolved": "https://registry.npmjs.org/@primer/components/-/components-30.3.0.tgz",
@@ -3669,22 +3684,22 @@
         "react": ">=15"
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+      "resolved": "https://registry.npmjs.org/@primer/primitives/-/primitives-4.8.1.tgz",
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+    },
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-      "dependencies": {
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+      "version": "21.5.1",
+      "resolved": "https://registry.npmjs.org/@primer/css/-/css-21.5.1.tgz",
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       "engines": {
-        "node": "^12.20.0 || ^14.13.1 || >=16.0.0"
+        "node": ">=16.0.0"
+      },
+      "peerDependencies": {
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-    "node_modules/@primer/css/node_modules/@primer/primitives": {
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-      "resolved": "https://registry.npmjs.org/@primer/primitives/-/primitives-4.7.0.tgz",
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@@ -3705,9 +3720,29 @@
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+      "version": "9.1.2",
+      "resolved": "https://registry.npmjs.org/@primer/primitives/-/primitives-9.1.2.tgz",
+      "integrity": "sha512-KecRJpUdIf14J3gVpoyMMJeQD6Sh5kcHk93N5bYch4XGB0GOZP3ypxz+NByMjr/2HHPsRfCCO5EEgNjmeWYUGQ==",
+      "peer": true,
+      "dependencies": {
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+        "prettier": "3.3"
+      }
+    },
+    "node_modules/@primer/primitives/node_modules/prettier": {
+      "version": "3.3.3",
+      "resolved": "https://registry.npmjs.org/prettier/-/prettier-3.3.3.tgz",
+      "integrity": "sha512-i2tDNA0O5IrMO757lfrdQZCc2jPNDVntV0m/+4whiDfWaTKfMNgR7Qz0NAeGz/nRqF4m5/6CLzbP4/liHt12Ew==",
+      "peer": true,
+      "bin": {
+        "prettier": "bin/prettier.cjs"
+      },
+      "engines": {
+        "node": ">=14"
+      },
+      "funding": {
+        "url": "https://github.com/prettier/prettier?sponsor=1"
+      }
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     "node_modules/@radix-ui/react-polymorphic": {
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@@ -15642,6 +15677,15 @@
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       "dev": true
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+    "node_modules/make-synchronized": {
+      "version": "0.2.9",
+      "resolved": "https://registry.npmjs.org/make-synchronized/-/make-synchronized-0.2.9.tgz",
+      "integrity": "sha512-4wczOs8SLuEdpEvp3vGo83wh8rjJ78UsIk7DIX5fxdfmfMJGog4bQzxfvOwq7Q3yCHLC4jp1urPHIxRS/A93gA==",
+      "peer": true,
+      "funding": {
+        "url": "https://github.com/fisker/make-synchronized?sponsor=1"
+      }
+    },
     "node_modules/makeerror": {
       "version": "1.0.11",
       "resolved": "https://registry.npmjs.org/makeerror/-/makeerror-1.0.11.tgz",
@@ -19427,7 +19471,6 @@
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-      "dev": true,
       "bin": {
         "prettier": "bin-prettier.js"
       },
@@ -28079,6 +28122,15 @@
         "@octokit/openapi-types": "^11.0.0"
       }
     },
+    "@prettier/sync": {
+      "version": "0.5.2",
+      "resolved": "https://registry.npmjs.org/@prettier/sync/-/sync-0.5.2.tgz",
+      "integrity": "sha512-Yb569su456XNx5BsH/Vyem7xD6g/y9iLmLUzRKM1a/dhU/D7HqqvkAG72znulXlMXztbV0iiu9O5AL8K98TzZQ==",
+      "peer": true,
+      "requires": {
+        "make-synchronized": "^0.2.8"
+      }
+    },
     "@primer/components": {
       "version": "30.3.0",
       "resolved": "https://registry.npmjs.org/@primer/components/-/components-30.3.0.tgz",
@@ -28108,23 +28160,19 @@
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+        },
+        "@primer/primitives": {
+          "version": "4.8.1",
+          "resolved": "https://registry.npmjs.org/@primer/primitives/-/primitives-4.8.1.tgz",
+          "integrity": "sha512-mgr6+EKpn4DixuhLt3drk7QmNQO8M7RYONWovg1nkV7p56jklhDLfZmp1luLUee37eQGAxx3ToStL6gqINFjnQ=="
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-      "resolved": "https://registry.npmjs.org/@primer/css/-/css-17.9.0.tgz",
-      "integrity": "sha512-/wnpDjw4LKU0iJ+maAP+a458unPrQGLXm3wU7pGG9jmbyTnoIaggxVQljAC3X2DRPkrL0QCShlltUBuZV1PIeA==",
-      "requires": {
-        "@primer/primitives": "4.7.0"
-      },
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-        "@primer/primitives": {
-          "version": "4.7.0",
-          "resolved": "https://registry.npmjs.org/@primer/primitives/-/primitives-4.7.0.tgz",
-          "integrity": "sha512-0tvy4e412UvwdhOIcLQU7N3TRA/SFzCcIBB0oReIwnaR+tIeSHqxoPaoHA3WZPjZpSOcvJiURmA5EXcZnFkGmg=="
-        }
-      }
+      "version": "21.5.1",
+      "resolved": "https://registry.npmjs.org/@primer/css/-/css-21.5.1.tgz",
+      "integrity": "sha512-/dw7P2eHbLEq77E6WVhVPud/HtyzAzlQgX6f8HQ/i0l1r5EZeh9r7/THgMUt0MgdSlJb7t+WT+V+zN8EDkU9mw==",
+      "requires": {}
     },
     "@primer/octicons": {
       "version": "15.1.0",
@@ -28141,9 +28189,22 @@
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-      "resolved": "https://registry.npmjs.org/@primer/primitives/-/primitives-4.8.1.tgz",
-      "integrity": "sha512-mgr6+EKpn4DixuhLt3drk7QmNQO8M7RYONWovg1nkV7p56jklhDLfZmp1luLUee37eQGAxx3ToStL6gqINFjnQ=="
+      "version": "9.1.2",
+      "resolved": "https://registry.npmjs.org/@primer/primitives/-/primitives-9.1.2.tgz",
+      "integrity": "sha512-KecRJpUdIf14J3gVpoyMMJeQD6Sh5kcHk93N5bYch4XGB0GOZP3ypxz+NByMjr/2HHPsRfCCO5EEgNjmeWYUGQ==",
+      "peer": true,
+      "requires": {
+        "@prettier/sync": "^0.5.2",
+        "prettier": "3.3"
+      },
+      "dependencies": {
+        "prettier": {
+          "version": "3.3.3",
+          "resolved": "https://registry.npmjs.org/prettier/-/prettier-3.3.3.tgz",
+          "integrity": "sha512-i2tDNA0O5IrMO757lfrdQZCc2jPNDVntV0m/+4whiDfWaTKfMNgR7Qz0NAeGz/nRqF4m5/6CLzbP4/liHt12Ew==",
+          "peer": true
+        }
+      }
     },
     "@radix-ui/react-polymorphic": {
       "version": "0.0.14",
@@ -37616,6 +37677,12 @@
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       "dev": true
     },
+    "make-synchronized": {
+      "version": "0.2.9",
+      "resolved": "https://registry.npmjs.org/make-synchronized/-/make-synchronized-0.2.9.tgz",
+      "integrity": "sha512-4wczOs8SLuEdpEvp3vGo83wh8rjJ78UsIk7DIX5fxdfmfMJGog4bQzxfvOwq7Q3yCHLC4jp1urPHIxRS/A93gA==",
+      "peer": true
+    },
     "makeerror": {
       "version": "1.0.11",
       "resolved": "https://registry.npmjs.org/makeerror/-/makeerror-1.0.11.tgz",
@@ -40505,8 +40572,7 @@
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-      "dev": true
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diff --git a/package.json b/package.json
index f27d53d4ddcf..156328a13b22 100644
--- a/package.json
+++ b/package.json
@@ -12,7 +12,7 @@
     "@alex_neo/jest-expect-message": "^1.0.5",
     "@hapi/accept": "^5.0.2",
     "@primer/components": "^30.3.0",
-    "@primer/css": "^17.9.0",
+    "@primer/css": "^21.5.1",
     "@primer/octicons": "^15.1.0",
     "@primer/octicons-react": "^15.1.0",
     "accept-language-parser": "^1.5.0",