Center selector component horizontally

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: chtitux

src/style.css

@@ -3,6 +3,7 @@
 .rgs-selector {
   font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
   max-width: 600px;
+  margin: 0 auto;
   border: 1px solid #ddd;
   border-radius: 8px;
   background: #fff;