fix: Add initial position to platformer player character

Player was invisible because CSS lacked initial left/bottom position.
Added explicit positioning and z-index to ensure visibility.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: canerdogan

docs-site/static/demos/platformer-tutorial.html

@@ -47,6 +47,9 @@
             background: linear-gradient(180deg, #6366f1, #4f46e5);
             border-radius: 6px 6px 2px 2px;
             transition: left 0.05s linear;
+            left: 50px;
+            bottom: 40px;
+            z-index: 10;
         }
         .player::before {
             content: '👀';