feat: add search box to 404 page

layouts/404.html

@@ -1,19 +1,29 @@
 {{ partial "header.html" . }}
 {{ partial "navbar.html" . }}
-<div class="container">
+<div class="universal-wrapper pt-3">
 
   <h1>{{ i18n "page_not_found" }}</h1>
+
+  {{/* Show search box if Academic's search engine is enabled. */}}
+  {{ if eq site.Params.search.engine 1 }}
+  <form class="d-flex align-items-center mb-3">
+    <input name="q" type="search" class="form-control" id="search-query" placeholder="{{ i18n "search_placeholder" }}" autocomplete="off">
+  </form>
+  {{ end }}
+
+  {{/* Suggest recently published pages to the user. */}}
+
   <p>{{ i18n "404_recommendations" }}</p>
 
   {{ $query := site.RegularPages }}
   {{ $count := len $query }}
   {{ if gt $count 0 }}
-    <h2>{{ i18n "user_profile_latest" }}</h2>
+  <h2>{{ i18n "user_profile_latest" }}</h2>
+  <ul>
     {{ range first 10 $query }}
-    <ul>
       <li><a href="{{ .RelPermalink }}">{{ .Title }}</a></li>
-    </ul>
     {{ end }}
+  </ul>
   {{ end }}
 
 </div>