Improve site layout and center content across mobile and desktop views

Updates CSS to center content and icons on various pages (competitions, contact, contributors, sponsors) and adjusts horizontal rule styling. Modifies HTML structure in competitions.html for better content organization.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 5e584ab0-c340-4432-97ef-1972582b60e9
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Event-Id: 07c2b9b6-4a76-4da2-ad04-fcaacb16832a
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/d0a1d46d-d203-4308-bc6a-312ac7c0243b/5e584ab0-c340-4432-97ef-1972582b60e9/SuPUNrT

static/css/styles.css

@@ -428,8 +428,9 @@ hr {
     transform: translate(-50%, -50%);
     z-index: 2;
     max-width: 800px;
-    width: 90%;
+    width: 88%;
     text-align: center;
+    padding: 0 16px;
 }
 
 .hero-title {
@@ -477,7 +478,10 @@ hr {
     border: 1px solid rgba(255, 255, 255, 0.08);
     border-radius: 16px;
     padding: 32px;
-    text-align: left;
+    text-align: center;
+    display: flex;
+    flex-direction: column;
+    align-items: center;
 }
 
 .stats-icon {
@@ -486,7 +490,7 @@ hr {
     display: flex;
     align-items: center;
     justify-content: center;
-    margin-bottom: 16px;
+    margin: 0 auto 16px auto;
     color: var(--white);
 }