adding js toggle for light-dark theme

js/app.js

@@ -1,3 +1,5 @@
+// Menu system
+
   const body = document.body;
   const menuToggle = document.getElementById('menuToggle');
   const menuClose = document.getElementById('menuClose');
@@ -54,4 +56,76 @@
 	if (window.innerWidth >= 768 && body.classList.contains('menu-open')) {
 	  closeMenu();
 	}
-  });
+  });
+  
+  // light-dark toggle
+  
+const STORAGE_KEY = 'theme-preference';
+  const root = document.documentElement;
+  const mq = window.matchMedia('(prefers-color-scheme: dark)');
+  
+  function getSystemTheme() {
+	return mq.matches ? 'dark' : 'light';
+  }
+  
+  function getSavedTheme() {
+	try {
+	  return localStorage.getItem(STORAGE_KEY) || 'system';
+	} catch {
+	  return 'system';
+	}
+  }
+  
+  function setSavedTheme(value) {
+	try {
+	  localStorage.setItem(STORAGE_KEY, value);
+	} catch {}
+  }
+  
+  function applyTheme(theme = getSavedTheme()) {
+	root.style.colorScheme = theme === 'system' ? 'light dark' : theme;
+  }
+  
+  function getNextTheme() {
+	return getSavedTheme() === 'system'
+	  ? (getSystemTheme() === 'dark' ? 'light' : 'dark')
+	  : 'system';
+  }
+  
+  function updateButton() {
+	const btn = document.getElementById('theme-toggle');
+	if (!btn) return;
+  
+	const theme = getSavedTheme();
+	// btn.textContent =
+	//   theme === 'system'
+	// 	? `Use ${getSystemTheme() === 'dark' ? 'light' : 'dark'} theme`
+	// 	: 'Use browser/OS theme';
+  }
+  
+  function toggleTheme() {
+	setSavedTheme(getNextTheme());
+	applyTheme();
+	updateButton();
+  }
+  
+  function initThemeToggle() {
+	applyTheme();
+	updateButton();
+  
+	const btn = document.getElementById('theme-toggle');
+	if (btn) btn.addEventListener('click', toggleTheme);
+  
+	mq.addEventListener('change', () => {
+	  if (getSavedTheme() === 'system') {
+		applyTheme('system');
+		updateButton();
+	  }
+	});
+  }
+  
+  if (document.readyState === 'loading') {
+	document.addEventListener('DOMContentLoaded', initThemeToggle);
+  } else {
+	initThemeToggle();
+  }