[docs] Fix 301 link

docs/data/toolpad/core/components/app-provider/app-provider.md

@@ -80,7 +80,7 @@ export default function App(props) {
 
 An `AppProvider` can set a visual theme for all elements inside it to adopt via the `theme` prop. This prop can be set in a few distinct ways with different advantages and disadvantages:
 
-1. [CSS variables theme](https://mui.com/material-ui/experimental-api/css-theme-variables/overview/): the default and recommended theming option for Toolpad applications, as it is the only option that prevents issues such as [dark-mode SSR flickering](https://github.com/mui/material-ui/issues/27651) and supports both light and dark mode with a single theme definition. The provided default theme in Toolpad is already in this format. **CSS variables themes are only supported when you use `@toolpad/core` with version 5.x of `@mui/material`.**
+1. [CSS variables theme](https://mui.com/material-ui/customization/css-theme-variables/overview/): the default and recommended theming option for Toolpad applications, as it is the only option that prevents issues such as [dark-mode SSR flickering](https://github.com/mui/material-ui/issues/27651) and supports both light and dark mode with a single theme definition. The provided default theme in Toolpad is already in this format. **CSS variables themes are only supported when you use `@toolpad/core` with version 5.x of `@mui/material`.**
 2. [Standard Material UI theme](https://mui.com/material-ui/customization/theming/): a single standard Material UI theme can be provided as the only theme to be used.
 3. **Light and dark themes**: two separate Material UI themes can be provided for light and dark mode in an object with the format `{ light: Theme, dark: Theme }`
 

docs/translations/api-docs/app-provider/app-provider.json

@@ -8,7 +8,7 @@
     "router": { "description": "Router implementation used inside Toolpad components." },
     "session": { "description": "Session info about the current user." },
     "theme": {
-      "description": "<a href=\"https://mui.com/toolpad/core/react-app-provider/#theming\">Theme or themes</a> to be used by the app in light/dark mode. A <a href=\"https://mui.com/material-ui/experimental-api/css-theme-variables/overview/\">CSS variables theme</a> is recommended."
+      "description": "<a href=\"https://mui.com/toolpad/core/react-app-provider/#theming\">Theme or themes</a> to be used by the app in light/dark mode. A <a href=\"https://mui.com/material-ui/customization/css-theme-variables/overview/\">CSS variables theme</a> is recommended."
     },
     "window": {
       "description": "The window where the application is rendered. This is needed when rendering the app inside an iframe, for example."

packages/toolpad-core/src/AppProvider/AppProvider.tsx

@@ -83,7 +83,7 @@ export interface AppProviderProps {
    */
   children: React.ReactNode;
   /**
-   * [Theme or themes](https://mui.com/toolpad/core/react-app-provider/#theming) to be used by the app in light/dark mode. A [CSS variables theme](https://mui.com/material-ui/experimental-api/css-theme-variables/overview/) is recommended.
+   * [Theme or themes](https://mui.com/toolpad/core/react-app-provider/#theming) to be used by the app in light/dark mode. A [CSS variables theme](https://mui.com/material-ui/customization/css-theme-variables/overview/) is recommended.
    * @default createTheme()
    */
   theme?: AppTheme;
@@ -257,7 +257,7 @@ AppProvider.propTypes /* remove-proptypes */ = {
     }),
   }),
   /**
-   * [Theme or themes](https://mui.com/toolpad/core/react-app-provider/#theming) to be used by the app in light/dark mode. A [CSS variables theme](https://mui.com/material-ui/experimental-api/css-theme-variables/overview/) is recommended.
+   * [Theme or themes](https://mui.com/toolpad/core/react-app-provider/#theming) to be used by the app in light/dark mode. A [CSS variables theme](https://mui.com/material-ui/customization/css-theme-variables/overview/) is recommended.
    * @default createTheme()
    */
   theme: PropTypes.object,