未重写之前：

 会显示当前网站的 url 作为 title 主题

 可利用 js 对 alert 进行重写。只可去掉 url 主题，不可自定义。

代码如下 ：

js 代码：

window.alert = function(msg, callback) {    var div = document.createElement("div");
    div.innerHTML = "<style type=\"text/css\">"
            + ".nbaMask { position: fixed; z-index: 1000; top: 0; right: 0; left: 0; bottom: 0; background: rgba(0, 0, 0, 0.5); }                                                                                                                                                                       "
            + ".nbaMaskTransparent { position: fixed; z-index: 1000; top: 0; right: 0; left: 0; bottom: 0; }                                                                                                                                                                                            "
            + ".nbaDialog { position: fixed; z-index: 5000; width: 80%; max-width: 300px; top: 50%; left: 50%; -webkit-transform: translate(-50%, -50%); transform: translate(-50%, -50%); background-color: #fff; text-align: center; border-radius: 8px; overflow: hidden; opacity: 1; color: white; }"
            + ".nbaDialog .nbaDialogHd { padding: .2rem .27rem .08rem .27rem; }                                                                                                                                                                                                                         "
            + ".nbaDialog .nbaDialogHd .nbaDialogTitle { font-size: 17px; font-weight: 400; }                                                                                                                                                                                                           "
            + ".nbaDialog .nbaDialogBd { padding: 0 .27rem; font-size: 15px; line-height: 1.3; word-wrap: break-word; word-break: break-all; color: #000000; }                                                                                                                                          "
            + ".nbaDialog .nbaDialogFt { position: relative; line-height: 48px; font-size: 17px; display: -webkit-box; display: -webkit-flex; display: flex; }                                                                                                                                          "
            + ".nbaDialog .nbaDialogFt:after { content: \" \"; position: absolute; left: 0; top: 0; right: 0; height: 1px; border-top: 1px solid #e6e6e6; color: #e6e6e6; -webkit-transform-origin: 0 0; transform-origin: 0 0; -webkit-transform: scaleY(0.5); transform: scaleY(0.5); }               "
            + ".nbaDialog .nbaDialogBtn { display: block; -webkit-box-flex: 1; -webkit-flex: 1; flex: 1; color: #09BB07; text-decoration: none; -webkit-tap-highlight-color: transparent; position: relative; margin-bottom: 0; }                                                                       "
            + ".nbaDialog .nbaDialogBtn:after { content: \" \"; position: absolute; left: 0; top: 0; width: 1px; bottom: 0; border-left: 1px solid #e6e6e6; color: #e6e6e6; -webkit-transform-origin: 0 0; transform-origin: 0 0; -webkit-transform: scaleX(0.5); transform: scaleX(0.5); }             "
            + ".nbaDialog a { text-decoration: none; -webkit-tap-highlight-color: transparent; }"
            + "</style>"
            + "<div id=\"dialogs2\" style=\"display: none\">"
            + "<div class=\"nbaMask\"></div>"
            + "<div class=\"nbaDialog\">"
            + "    <div class=\"nbaDialogHd\">"
            + "        <strong class=\"nbaDialogTitle\"></strong>"
            + "    </div>"
            + "    <div class=\"nbaDialogBd\" id=\"dialog_msg2\">弹窗内容，告知当前状态、信息和解决方法，描述文字尽量控制在三行内</div>"
            + "    <div class=\"nbaDialogHd\">"
            + "        <strong class=\"nbaDialogTitle\"></strong>"
            + "    </div>"
            + "    <div class=\"nbaDialogFt\">"
            + "        <a href=\"javascript:;\" class=\"nbaDialogBtn nbaDialogBtnPrimary\" id=\"dialog_ok2\">确定</a>"
            + "    </div></div></div>";
    document.body.appendChild(div); 
    var dialogs2 = document.getElementById("dialogs2");
    dialogs2.style.display = 'block'; 
    var dialog_msg2 = document.getElementById("dialog_msg2");
    dialog_msg2.innerHTML = msg; 
    // var dialog_cancel = document.getElementById("dialog_cancel");
    // dialog_cancel.onclick = function() {
    // dialogs2.style.display = 'none';
    // };
    var dialog_ok2 = document.getElementById("dialog_ok2");
    dialog_ok2.onclick = function() {
        dialogs2.style.display = 'none';
        callback();
    };
};

 html 引用：（当然，可以不进行引用，直接将 js 代码放在 html 页面中   script  标签当中也可）

<!DOCTYPE html><html><head><title>alert.html</title><meta charset="UTF-8"><meta name="keywords" content="keyword1,keyword2,keyword3"><meta name="description" content="this is my page"><meta name="content-type" content="text/html; charset=UTF-8"><!--<link rel="stylesheet" type="text/css" href="./styles.css">-->
 </head><body>
    This is my HTML page.    <br>
    <script type="text/javascript" src="alert.js"></script>
    <script type="text/javascript">
        alert("哈哈哈！！！看，没有标题~_~");    </script></body></html>

重写后样式：