web: add manta ray as demo animal

Author: sibgit

css/main.css

@@ -26,7 +26,7 @@ p {
 ul {
 	display: grid;
 	grid-template-columns: repeat(2, auto); /* Two equal-width columns */
-	grid-template-rows: repeat(7, auto);
+	grid-template-rows: repeat(8, auto);
 	grid-auto-flow: column;
 	max-width: 1000px;
 	gap: 10px; /* Space between items */

index.html

@@ -14,6 +14,7 @@ <h1>Awesome Animal Awareness Project</h1>
             <li><a href="gorilla.html">Gorilla</a></li>
             <li><a href="honey_badger.html">Honey Badger</a></li>
             <li><a href="kiwi_bird.html">Kiwi bird</a></li>
+            <li><a href="manta_ray.html">Manta ray (demo animal)</a></li>
             <li><a href="octopus.html">Octopus</a></li>
             <li><a href="pallas_cat.html">Pallas's cat</a></li>
             <li><a href="platypus.html">Platypus</a></li>