Adjust competition cards to use more screen space on mobile devices

Modify CSS in static/css/styles.css to remove background and borders from .competitions .content-container and set competition cards to 90% width with auto margins for mobile responsiveness.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 5e584ab0-c340-4432-97ef-1972582b60e9
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Event-Id: 93b5b5b0-b027-4625-9449-395e19a12f66
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/d0a1d46d-d203-4308-bc6a-312ac7c0243b/5e584ab0-c340-4432-97ef-1972582b60e9/36EEkkQ

static/css/styles.css

@@ -1396,9 +1396,21 @@ span.emoji:hover::after {
         margin-top: 70px;
     }
 
+    .competitions .content-container {
+        background: transparent;
+        backdrop-filter: none;
+        -webkit-backdrop-filter: none;
+        border: none;
+        padding: 0;
+        margin: 0;
+    }
+
     .competition-card {
         padding: 24px;
         margin-bottom: 24px;
+        width: 90%;
+        margin-left: auto;
+        margin-right: auto;
     }
 
     .card-container,