Fix heading level issue by mirorauhala · Pull Request #7

Fix heading level issue by mirorauhala · Pull Request #7 · reactjs/fi.react.dev

The third heading level caused an error on JavaScript in JSX with curly braces.

TypeError: Cannot read properties of undefined (reading 'current') at src/components/MDX/Challenges/Navigation.tsx (68:44)

Changing to the fourth heading level fixes this. This PR also fixes the heading level for Importing and exporting components, where the heading level caused scroll jumps.