fix: Improve mobile modal visibility and button alignment

- Center download button text with justify-content
- Set header text to solid black (#000) for better visibility
- Darken close button background for better contrast
- Remove any disabled appearance on mobile

Fixes grayed-out/disabled look and left-aligned button text on mobile.

static/css/04-interactive/_modals.css

@@ -857,6 +857,7 @@
         padding: 10px 20px;
         font-size: 0.9rem;
         width: 100%;
+        justify-content: center;
     }
 
     /* Reduce footer padding */
@@ -864,6 +865,21 @@
         padding-top: 0.75rem;
         margin-top: 0.5rem;
     }
+
+    /* Ensure header and close button are clearly visible */
+    .info-modal-header h2 {
+        color: #000;
+        opacity: 1;
+    }
+
+    .info-modal-close {
+        background: rgba(0, 0, 0, 0.08);
+        color: #000;
+    }
+
+    .info-modal-close:hover {
+        background: rgba(0, 0, 0, 0.15);
+    }
 }
 
 /* =============================================================================