✨ Implemented dark theme.

Signed-off-by: Edoardo Odorico <edoubuntu@gmail.com>

public/views/hackmd/header.ejs

@@ -96,6 +96,11 @@
                     <input type="radio" name="mode" autocomplete="off"><i class="fa fa-pencil"></i>
                 </label>
             </div>
+            <div class="btn-group" data-toggle="buttons">
+                <label class="btn ui-night" title="<%= __('Night Theme') %>">
+                    <input type="checkbox" name="night"><i class="fa fa-moon-o"></i>
+                </label>
+            </div>
             <span class="btn btn-link btn-file ui-help" title="<%= __('Help') %>" data-toggle="modal" data-target=".help-modal">
                 <i class="fa fa-question-circle"></i>
             </span>