[#1] Add default theme env variable

web/src/components/ThemeToggle/ThemeToggle.tsx

@@ -8,7 +8,10 @@ const DARK_THEME = 'dark'
 
 const ThemeToggle = () => {
   const [theme, setTheme] = useState(
-    localStorage.getItem('theme') ?? LIGHT_THEME
+    localStorage.getItem('theme') ||
+      ([LIGHT_THEME, DARK_THEME].includes(process.env.DEFAULT_THEME)
+        ? process.env.DEFAULT_THEME
+        : LIGHT_THEME)
   )
 
   const handleToggle = (e: React.ChangeEvent<HTMLInputElement>) => {

web/src/entry.client.tsx

@@ -8,6 +8,11 @@ import App from 'src/App'
  * rather than replacing it.
  * https://react.dev/reference/react-dom/client/hydrateRoot
  */
+enum Theme {
+  light = 'light',
+  dark = 'dark',
+}
+
 const redwoodAppElement = document.getElementById('redwood-app')
 
 if (!redwoodAppElement)
@@ -21,6 +26,11 @@ if (!hasFlag(process.env.COUNTRY))
     'Invalid COUNTRY environment variable, please select a valid ISO-3166-1 alpha-2 country code\n See https://en.wikipedia.org/wiki/ISO_3166-1#Codes'
   )
 
+if (!(process.env.DEFAULT_THEME.toLowerCase() in Theme))
+  throw new Error(
+    'Invalid DEFAULT_THEME environment variable, please select either light or dark'
+  )
+
 if (redwoodAppElement.children?.length > 0)
   hydrateRoot(redwoodAppElement, <App />)
 else {