fix: update link to CSS file for Pixels theme documentation

Author: estruyf

docs/src/content/docs/slides/themes/pixels.mdx

@@ -54,7 +54,7 @@ theme: pixels
 
 ## CSS
 
-Here you can check the CSS of the [Pixels theme](https://github.com/estruyf/vscode-demo-time/blob/main/apps/webviews/src/themes/pixels.css).
+Here you can check the CSS of the [Pixels theme](https://github.com/estruyf/vscode-demo-time/tree/main/apps/webviews/src/themes/pixels.css).
 
 ### CSS variables