Fix broken tabs

Was too overzealous deleting stuff in #8058

Author: poteto

src/content/reference/react-dom/createPortal.md

@@ -398,7 +398,7 @@ Here is a complete example you can play with:
 }
 ```
 
-```js
+```js src/App.js
 import { useRef, useEffect, useState } from 'react';
 import { createPortal } from 'react-dom';
 import { createMapWidget, addPopupToMapWidget } from './map-widget.js';

src/content/reference/react/useLayoutEffect.md

@@ -87,7 +87,7 @@ To do this, you need to render in two passes:
 
 **All of this needs to happen before the browser repaints the screen.** You don't want the user to see the tooltip moving. Call `useLayoutEffect` to perform the layout measurements before the browser repaints the screen:
 
-```js
+```js {5-8}
 function Tooltip() {
   const ref = useRef(null);
   const [tooltipHeight, setTooltipHeight] = useState(0); // You don't know real height yet
@@ -187,7 +187,7 @@ export default function ButtonWithTooltip({ tooltipContent, ...rest }) {
 }
 ```
 
-```js
+```js src/Tooltip.js active
 import { useRef, useLayoutEffect, useState } from 'react';
 import { createPortal } from 'react-dom';
 import TooltipContainer from './TooltipContainer.js';
@@ -337,7 +337,7 @@ export default function ButtonWithTooltip({ tooltipContent, ...rest }) {
 }
 ```
 
-```js
+```js src/Tooltip.js active
 import { useRef, useLayoutEffect, useState } from 'react';
 import { createPortal } from 'react-dom';
 import TooltipContainer from './TooltipContainer.js';
@@ -484,7 +484,7 @@ export default function ButtonWithTooltip({ tooltipContent, ...rest }) {
 }
 ```
 
-```js
+```js src/Tooltip.js active
 import { useRef, useEffect, useState } from 'react';
 import { createPortal } from 'react-dom';
 import TooltipContainer from './TooltipContainer.js';

src/content/reference/react/useMemo.md

@@ -225,7 +225,7 @@ export default function App() {
 
 ```
 
-```js
+```js src/TodoList.js active
 import { useMemo } from 'react';
 import { filterTodos } from './utils.js'