docs: prevent initial loading flicker

Author: ctron

guide/theme/pagetoc.css

@@ -1,3 +1,11 @@
+#content > main {
+    display: none;
+}
+
+#content > main.wrapped {
+    display: revert;
+}
+
 :root {
     --toc-width: 270px;
     --center-content-toc-shift: calc(-1 * var(--toc-width) / 2);

guide/theme/pagetoc.js

@@ -20,6 +20,7 @@ function autoCreatePagetoc() {
   content.append(...main.childNodes);
 
   main.appendChild(content);
+  main.classList.add("wrapped");
 
   main.insertAdjacentHTML("beforeend", `
     <div class="sidetoc">