Support for rgb|rgba(*) format (#20800)

Author: deven96

src/content/partials/images/background.mdx

@@ -13,11 +13,19 @@ Background color to add underneath the image. Applies to images with transparenc
     OR
 
     background=red
-    ```
+
+		OR
+		
+		background= rgb%28240%2C40%2C145%29
+		```
   </TabItem>
   <TabItem label="Workers">
   ```js
   cf: {image: {background: "#RRGGBB"}}
+
+	OR
+
+	cf:{image: {background: "rgba(240,40,145,0)"}}
   ```
   </TabItem>
 </Tabs>