update fontSize

Author: alexcarpenter

docs/customization/variables.mdx

@@ -123,7 +123,7 @@ The `variables` property is used to adjust the general styles of the component's
   ---
 
   - `fontSize`
-  - `string`
+  - `string` | `{xs: string, sm: string, md: string, lg: string, xl: string}`
 
   The font size used throughout the components. By default, this is set to `0.8125rem`.