Update background image positioning in multiple components: Change background image class from 'absolute' to 'fixed' in AdminPage, ChallengesSection, and BackgroundSection for improved layout consistency.

components/challenges/ChallengesSection.tsx

@@ -140,7 +140,7 @@ export default function ChallengesSection({
     <section className="relative w-full min-h-screen flex flex-col items-center overflow-hidden pt-24 pb-16">
       {/* Background Image */}
       <div
-        className="absolute inset-0 bg-cover bg-center bg-no-repeat"
+        className="fixed inset-0 bg-cover bg-center bg-no-repeat"
         style={{
           backgroundImage: `url('${backgroundImage}')`,
         }}