diff --git a/docs/reference-guides/theme-json-reference/theme-json-living.md b/docs/reference-guides/theme-json-reference/theme-json-living.md
index cf7624766c9ff3..a694cf63e909fa 100644
--- a/docs/reference-guides/theme-json-reference/theme-json-living.md
+++ b/docs/reference-guides/theme-json-reference/theme-json-living.md
@@ -225,6 +225,13 @@ Outline styles.
 | style | string |  |
 | width | string |  |
 
+---
+
+### css
+
+Sets custom CSS to apply styling not covered by other theme.json properties.
+
+
 ---
 
 <!-- END TOKEN Autogenerated - DO NOT EDIT -->
diff --git a/schemas/json/theme.json b/schemas/json/theme.json
index d42706bec8df96..1a8aa67b0967b1 100644
--- a/schemas/json/theme.json
+++ b/schemas/json/theme.json
@@ -1169,6 +1169,10 @@
 						}
 					},
 					"additionalProperties": false
+				},
+				"css": {
+					"description": "Sets custom CSS to apply styling not covered by other theme.json properties.",
+					"type": "string"
 				}
 			}
 		},
@@ -1186,7 +1190,8 @@
 						"typography": {},
 						"filter": {},
 						"shadow": {},
-						"outline": {}
+						"outline": {},
+						"css": {}
 					},
 					"additionalProperties": false
 				}
@@ -1210,6 +1215,7 @@
 								"outline": {},
 								"spacing": {},
 								"typography": {},
+								"css": {},
 								":hover": {
 									"$ref": "#/definitions/stylesPropertiesComplete"
 								},
@@ -1561,6 +1567,7 @@
 						"filter": {},
 						"shadow": {},
 						"outline": {},
+						"css": {},
 						"elements": {
 							"$ref": "#/definitions/stylesElementsPropertiesComplete"
 						}
@@ -1629,6 +1636,7 @@
 						"filter": {},
 						"shadow": {},
 						"outline": {},
+						"css": {},
 						"elements": {
 							"description": "Styles defined on a per-element basis using the element's selector.",
 							"$ref": "#/definitions/stylesElementsPropertiesComplete"