refactor: add subtle border to publication date

- Add subtle white border with 20% opacity
- Rounded corners (6px border-radius)
- Helps define the date element without being too prominent

src/index.css

@@ -550,6 +550,8 @@ body {
   color: #fff;
   padding: 0.4rem 0.75rem;
   text-shadow: 0 2px 4px rgba(0, 0, 0, 0.5);
+  border: 1px solid rgba(255, 255, 255, 0.2);
+  border-radius: 6px;
   z-index: 10;
 }