div 可视化区域弹窗居中

效果：

css:

.div_alt {
    position: fixed;
    border-radius: 5px;
    top: 50%;
    left: 50%;
    width: auto;
    min-width: 600px;
    min-height: 400px;
    height: auto;
    background: #fff;
    z-index: 10;
    display: none;
    box-shadow: 1px 1px 50px rgba(0,0,0,.3);
}

    .div_alt .title {
        width: 100%;
        position: relative;
        border-radius: 5px 0 0 0;
        font-weight:bold;
        text-align:center;
        height: 45px;
        line-height: 45px;
        font-size: 16px;
        border-bottom: 2px solid #00994D;
        letter-spacing:2px;
        
    }

        .div_alt .title span {
            display: block;
            line-height: 60px;
            text-align: center;
            color: #fff;
            font-size: 24px;
        }

    .div_alt .div_p {
        /*padding: 20px 0;*/
    }

html:

 <div id="addRoute" class="div_alt" style="display: none;">
            <div class="title">
                添加行程
            </div>
            <div class="search">
                <table style=" 95%; margin: 0px auto;">
                    <tr>
                        <td class="name">行程主题：</td>
                        <td class="value">
                            <input type="text" id="txtRouteSubject" runat="server" maxlength="50" />
                            <span style="color: red;">&nbsp;&nbsp;*</span>
                        </td>
                        <td style=" 25%"></td>
                    </tr>
                    <tr>
                        <td class="name">地址：</td>
                        <td class="value">
                            <input type="text" id="txtRouteAddress" runat="server" maxlength="50" />
                            <span style="color: red;">&nbsp;&nbsp;*</span>
                        </td>
                        <td></td>
                    </tr>
                    <tr>
                        <td class="name">开始时间：</td>
                        <td class="value"  colspan="2">
                            <uc1:DateUC ID="ducRouteStarttime" runat="server" Width="125" ShowTime="true" />
                            <uc1:DateUC ID="ducRouteStoptime" runat="server" Width="125" ShowTime="true" />
                            <span style="color: red;">&nbsp;&nbsp;*</span>
                        </td>
                    </tr>
                    <tr>
                        <td class="name">内容：</td>
                        <td class="value">
                            <textarea runat="server" maxlength="200" id="txtRouteContent" rows="6" cols="30"></textarea>
                            <span style="color: red;">&nbsp;&nbsp;*</span>
                        </td>
                        <td></td>
                    </tr>
                    <tr>
                        <td colspan="3" class="tc">
                            <input type="button" id="btnRouteSave" value="添加" />&nbsp;&nbsp;&nbsp;&nbsp;
                        <input type="button" id="btnRouteCancel" value="返回" />
                        </td>
                    </tr>
                </table>
                <input type="hidden" id="routeaction" value="a" />
            </div>
        </div>

js:

function show() {
    var $div = $('#addRoute');
    var top = (window.outerHeight - $div.outerHeight()) / 2;
    var left = (window.outerWidth - $div.outerWidth()) / 2;
    $div.css({ "z-index": "1000", "top": top, "left": left }).show();
    $('#div_alt_bg').css("z-index", "999").show();
}