Make demo editor reponsive to color scheme changes

It was already using the appropriate theme, but now it also updates if
the color scheme preference changes

Author: remcohaszing

examples/demo/src/index.ts

@@ -102,10 +102,15 @@ formatting:       Formatting is supported too! Under the hood this is powered by
 
 `.replace(/:$/m, ': ')
 
+const dark = matchMedia('(prefers-color-scheme: dark)')
+editor.setTheme(dark.matches ? 'vs-dark' : 'vs-light')
+dark.addEventListener('change', () => {
+  editor.setTheme(dark.matches ? 'vs-dark' : 'vs-light')
+})
+
 const ed = editor.create(document.getElementById('editor')!, {
   automaticLayout: true,
   model: editor.createModel(value, 'yaml', Uri.parse('monaco-yaml.yaml')),
-  theme: window.matchMedia('(prefers-color-scheme: dark)').matches ? 'vs-dark' : 'vs-light',
   quickSuggestions: {
     other: true,
     comments: false,