Refactor 404 error page to use div instead of p for search form

The search form on the 404 error page was previously wrapped in a `<p>` tag, which is semantically incorrect as `<p>` tags cannot contain block-level elements like `<form>`. This commit refactors the page to use a `<div>` tag instead, which is a more appropriate container for the search form. This change improves the semantic structure of the page and avoids potential rendering issues.

Author: AndrewDongminYoo

CHANGELOG.md

@@ -1,6 +1,7 @@
 ## 8.3.4-wip
 * The URL for category pages now uses _category name_ instead of
   _category `displayName`_.
+* Refactor 404 error page to use div instead of p for search form.
 
 ## 8.3.3
 

lib/templates/404error.html

@@ -1,27 +1,39 @@
 {{>head}}
 
-  <div id="dartdoc-main-content" class="main-content">
-    <h1>404: Something's gone wrong :-(</h1>
+<div id="dartdoc-main-content" class="main-content">
+  <h1>404: Something's gone wrong :-(</h1>
 
-    <section class="desc">
-      <p>You've tried to visit a page that doesn't exist.  Luckily this site
-         has other <a href="index.html">pages</a>.</p>
-      <p>If you were looking for something specific, try searching:
+  <section class="desc">
+    <p>
+      You've tried to visit a page that doesn't exist. Luckily this site has
+      other <a href="index.html">pages</a>.
+    </p>
+    <div>
+      If you were looking for something specific, try searching:
       <form class="search-body" role="search">
-        <input type="text" id="search-body" autocomplete="off" disabled class="form-control typeahead" placeholder="Loading search...">
+        <input
+          type="text"
+          id="search-body"
+          autocomplete="off"
+          disabled
+          class="form-control typeahead"
+          placeholder="Loading search..."
+        />
       </form>
-      </p>
+    </div>
+  </section>
+</div>
+<!-- /.main-content -->
 
-    </section>
-  </div> <!-- /.main-content -->
+<div id="dartdoc-sidebar-left" class="sidebar sidebar-offcanvas-left">
+  {{>search_sidebar}}
+  <h5>
+    <span class="package-name">{{self.name}}</span>
+    <span class="package-kind">{{self.kind}}</span>
+  </h5>
+  {{>packages}}
+</div>
 
-  <div id="dartdoc-sidebar-left" class="sidebar sidebar-offcanvas-left">
-    {{>search_sidebar}}
-    <h5><span class="package-name">{{self.name}}</span> <span class="package-kind">{{self.kind}}</span></h5>
-    {{>packages}}
-  </div>
-
-  <div id="dartdoc-sidebar-right" class="sidebar sidebar-offcanvas-right">
-  </div>
+<div id="dartdoc-sidebar-right" class="sidebar sidebar-offcanvas-right"></div>
 
 {{>footer}}