initial work on sidenotes

src/routes/__layout.svelte

@@ -1,6 +1,10 @@
 <style>
+
+
     :global(main) {
-        max-width: 42rem;
+        --content-width: 42rem;
+        box-sizing: border-box;
+        max-width: var(--content-width);
         margin: 0 auto;
         padding:  0 15px;
     }