style: update header to midnight blue

app.py

@@ -280,14 +280,14 @@ custom_css = """
 .header {
     text-align: center;
     padding: 15px;
-    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
+    background: linear-gradient(135deg, #2d4a6f 0%, #1e3a5f 100%);
     color: white;
     border-radius: 10px;
     margin-bottom: 15px;
 }
 .header { position: relative; }
-.header h1 { margin: 0; font-size: 24px; }
-.header p { margin: 5px 0 0 0; opacity: 0.9; font-size: 14px; }
+.header h1 { margin: 0; font-size: 24px; color: white !important; }
+.header p { margin: 5px 0 0 0; opacity: 0.9; font-size: 14px; color: white !important; }
 .header .info-btn {
     display: inline-block;
     margin-top: 12px;