Update contribution.html

wiki/pages/contribution.html

@@ -14,7 +14,12 @@
     .header-title {
         font-family: 'New Courier', Courier, monospace; /* Updated font type for header */
         font-size: 24px; /* Updated font size for header */
-        color: #52be80; /* Header color */
+        color: black; /* Header color changed to black */
+    }
+    .sub-header {
+        font-family: 'New Courier', Courier, monospace; /* Updated font type for sub-header */
+        font-size: 24px; /* Updated font size for sub-header */
+        color: black; /* Sub-header color changed to black */
     }
 </style>