Update background color to use CSS variable and remove unused theme toggle logic

app/src/utils/theme.ts

@@ -20,12 +20,3 @@ export function toggleTheme() {
 
 // Initialize theme on page load
 setTheme();
-
-// Example: Call toggleTheme() when a button is clicked
-const toggleSwitch: Element | null = document.querySelector('#theme-switch');
-
-if (toggleSwitch) {
-    toggleSwitch.addEventListener('click', toggleTheme);
-} else {
-    console.warn("Theme switch button not found!");
-}