rename mdx file to fix all links

Author: LFDanLu

packages/dev/s2-docs/pages/s2/styling.mdx

@@ -10,8 +10,8 @@ export const section = 'Guides';
 export const tags = ['style', 'macro', 'spectrum', 'custom'];
 export const description = 'Styling in React Spectrum';
 export const relatedPages = [
-  {title: 'Advanced', url: './styling/Advanced.html'},
-  {title: 'Reference Table', url: './styling/Reference.html'}
+  {title: 'Advanced', url: './styling/advanced.html'},
+  {title: 'Reference Table', url: './styling/reference.html'}
 ];
 
 # Styling