Fix cannot use theme to override input variant

docs/Admin.md

@@ -275,7 +275,10 @@ See the [Theming documentation](./Theming.md#using-a-custom-menu) for more detai
 MUI supports [theming](https://mui.com/customization/themes). This lets you customize the look and feel of an admin by overriding fonts, colors, and spacing. You can provide a custom MUI theme by using the `theme` prop:
 
 ```jsx
+import { defaultTheme } from 'react-admin';
+
 const theme = {
+    ...defaultTheme,
     palette: {
         type: 'dark', // Switching the dark mode on is a single property value change.
     },
@@ -290,7 +293,7 @@ const App = () => (
 
 ![Dark theme](./img/dark-theme.png)
 
-For more details on predefined themes and custom themes, refer to the [MUI Customization documentation](https://mui.com/customization/themes/).
+For more details on predefined themes and custom themes, refer to [the Theming chapter](./Theming.md#global-theme-overrides) of the react-admin documentation.
 
 ## `layout`
 

docs/Inputs.md

@@ -268,6 +268,37 @@ import { FormDataConsumer } from 'react-admin';
  );
 ```
 
+### Overriding The Input Variant
+
+MUI offers [3 variants for text fields](https://mui.com/material-ui/react-text-field/#basic-textfield): `outlined`, `filled`, and `standard`. The default react-admin theme uses the `filled` variant. If you want your application to use another variant, override the `<Admin theme>` prop with a [custom theme](./Theming.md#global-theme-overrides), as follows:
+
+```jsx
+import { defaultTheme } from 'react-admin';
+
+const theme = {
+    ...defaultTheme,
+    components: {
+        ...defaultTheme.components,
+        MuiTextField: {
+            defaultProps: {
+                variant: 'outlined' as const,
+            },
+        },
+        MuiFormControl: {
+            defaultProps: {
+                variant: 'outlined' as const,
+            },
+        },
+    }
+};
+
+const App = () => (
+    <Admin theme={theme}>
+        // ...
+    </Admin>
+);
+```
+
 ## Writing Your Own Input Component
 
 If you need a more specific input type, you can write it directly in React. You'll have to rely on react-hook-form's [useController](https://react-hook-form.com/api/usecontroller) hook, to handle the value update cycle.

docs/Reference.md

@@ -203,7 +203,6 @@ title: "Reference"
 * `useSortState`
 * [`useStore`](./useStore.md)
 * [`useStoreContext`](./useStoreContext.md)
-* [`useStyles`](./Theming.md#overriding-a-component-style)
 * `useSuggestions`
 * [`useTheme`](./Theming.md#changing-the-theme-programmatically)
 * [`useTour`](https://marmelab.com/ra-enterprise/modules/ra-tour)<img class="icon" src="./img/premium.svg" />