add supporting components for sidenotes post

posts/sidenotes.mdx

@@ -6,7 +6,8 @@ draft: true
 ---
 
 import Sidenote from '@components/Sidenote.astro';
-import UnstyledSidenote from '@components/UnstyledSidenote.astro';
+import UnstyledSidenote from '@projects/sidenotes/UnstyledSidenote.astro';
+import '@projects/sidenotes/sidenote.css';
 
 One of my major goals when building this blog was to have sidenotes. I've always been a fan of sidenotes on the web, because the most comfortable reading width for a column of text is <em>far</em> less than the absurd amounts of screen width we tend to have available, and what else are we going to use it for?<Sidenote>Some sites use it for ads, of course, which is yet another example of how advertising ruins everything.</Sidenote>