效果如下:

编辑文件: /app/themes/Peafowl/header.php

找到

在下面添加:
    <!-- 顶部菜单 -->
    <li class="phone-hide pop-btn top-btn-el pop-btn-delayed">
        <a target="_blank" href="http://leanserver.top" class="top-btn-text"><span class="top-btn-text">官方博客</span></a>
    </li>

若需要添加通知选项可以参考下面代码

                        <!-- 系统提醒开始 -->
                        <li data-nav="notices" class="phone-hide pop-btn pop-keep-click">
                <span class="top-btn-text"><span class="icon icon-notification color-red"></span><span class="btn-text phone-hide phablet-hide">通知</span><span class="arrow-down"></span></span>
                                <div class="pop-box anchor-center c8 arrow-box arrow-box-top anchor-center">
                                        <div class="pop-box-inner padding-20">
                                                <ul class="list-style-type-decimal list-style-position-inside">
                                                        <li><a href="https://leanfan.com" target="_blank">[公告] 2019-02-16开放游客上传权限, 但建议登录后再上传, 方便查看以前的资料.</a>
                                                        <li><a href="https://leanfan.com" target="_blank">[完成] 2019-02-05 服务器升级. </a></li>
                                                        <li><a href="https://leanfan.com" target="_blank">[博客] 更新Oneindex</a>
</ul>               </div>
                           
                              </div>
                       </li>
                      <!-- 系统提醒完成 -->