style(component-preview): add border to preview box for enhanced visual definition

Author: azadshaikh

src/html/components/component-preview/component-preview.astro

@@ -68,7 +68,7 @@ const backgroundColor = bgColor ? 'var(--content-wrapper-bg)' : 'transparent'
 ---
 
 <div
-  class="card p-0 mb-4 preview-box"
+  class="card border p-0 mb-4 preview-box"
   data-toc-skip
   data-bg-color={bgColor.toString()}
   {...iframeSrc && { 'data-external-src': iframeSrc }}