导航栏不会写，各个元素定位乱掉了，老师帮忙看看，下拉菜单跟小三角

为什么下拉菜单跟三角形都设置的float：right, 为什么三角形在下拉菜单的左边，是先设置float的元素在最左边吗，导航栏的元素也太杂了吧，有没有整齐点的方法

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <link rel="stylesheet" href="css/style.css">
</head>
<body>
    <div class="registry">
        <!-- 导航栏 -->
        <header>
            <div class="header_wrap">
                <div class="header_logo">高铁客户服务中心<span> | </span><span>客户服务</span></div>
                <nav>
                    <span>意见反馈&nbsp;</span>
                    <a href="#">163.com</a>
                    <span>&nbsp;&nbsp;您好，请</span>
                    <a href="#">登录&nbsp;</a>
                    <span>|&nbsp;</span>
                    <a href="#">注册&nbsp;&nbsp;</a>
                    <div class="menu">
                        <span>我的IMOOC</span>
                        <ul class="menu-list">
                            <li>我的账户</li>
                            <li>已完成订单（改/退）</li>
                            <li>我的保险</li>
                            <li>查看个人信息</li>
                            <li>账户安全</li>
                            <li>常用联系人</li>
                            <li>重点旅客预约</li>
                            <li>遗失物品查找</li>
                        </ul>
                    </div>
                    <div class="arrow"></div>
                </nav>
                <div class="phone">
                    <a href="#">手机版</a>
                </div>  
            </div>
        </header>
        <!-- 表单栏 -->
        <div class="content">
            <h2>您现在的位置：<span>客运首页 > 注册</span></h2>
            <form action="">
                <h2>账户信息</h2>
                <P><span>*</span><span>用&nbsp;户&nbsp;名：</span><input type="text" placeholder="用户名设置成功后不可更改">&nbsp;&nbsp;<span class="prompt"></span></P>
 
                <P><span>*</span><span>登录密码：</span><input type="password" placeholder="6-20位字母、数字或符号">&nbsp;&nbsp;<span class="prompt"></span></P>
 
                <P><span>*</span><span>确认密码：</span><input type="password" placeholder="再次输入您的登录密码">&nbsp;&nbsp;<span class="prompt"></span></P>
 
                <P><span>*</span><span>姓&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;名：</span><input type="text" placeholder="请输入姓名">&nbsp;&nbsp;<span><a href="#">姓名填写规则</a></span></P>
 
                <P><span>*</span><span>证件类型：</span><select name="credit" id="credit"><option value="二代身份证">二代身份证</option></select>&nbsp;&nbsp;<span class="prompt"></span></P>
 
                <P><span>*</span><span>证件号码：</span><input type="text" placeholder="请输入您的证件号码">&nbsp;&nbsp;<span class="prompt"></span></P>
 
                <P><span></span><span>邮&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;箱：</span><input type="email" placeholder="请正确填写邮箱地址">&nbsp;&nbsp;<span class="prompt"></span></P>
 
                <P><span>*</span><span>手机号码：</span><input type="text" placeholder="请输入您的手机号码">&nbsp;&nbsp;<span class="prompt"></span></P>
 
                <P><span>*</span><span>旅客类型：</span><select name="people" id="people"><option value="成人">成人</option></select>&nbsp;&nbsp;<span class="prompt"></span></P>
 
                <p><input type="checkbox">我已阅读并同意遵守    <a href="">《中国铁路客户服务中心网站服务条款》</a></p>
 
                <input type="submit" id="sub" value="下一步">
            </form>
        </div>
            <!-- 页脚 -->
            <footer>
                <p>关于我们&nbsp;&nbsp;|&nbsp;&nbsp;网站声明</p>
                <p>Copyright © 2017 imooc.com All Rights Reserved | 京ICP备 13046642号-2</p>
            </footer>
 
         
    </div>
</body>
</html>

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    *{
    margin:0;
    padding: 0;
}
a{
    text-decoration: none;
    color: #000;
}
 
.registry{
    width: 100%;
    height:120px ;
    font-family: "Microsoft Yahei";
}
/* 导航栏 */
header{
    position: relative;
    background: #efefef;
    border-bottom:#2487c9 2px solid;
}
.header_wrap{ 
    position: relative;
    width: 1260px;
    height: 120px;
    margin: 0 auto;   
}
.header_logo{
    position: absolute;
    display: inline-block;
    width: 460px;
    height: 100px;
    background: url(../img/logo.png) left center no-repeat;
    line-height: 100px;
    font-size: 24px;
    text-indent: 120px;
    top:10px;
}
.header_logo>span:first-child{
    font-size:28px;
    font-weight: bolder;
}
.header_logo>span:last-child{
    font-size:20px;
    color:#66667b;
}
.header_logo>a:nth-child(2),.header_logo>a:nth-child(2){
    color:#fb7403;
}
/* 导航条 */
nav{
    position: absolute;
    right:100px;
    font-size: 16px;
    line-height: 120px;
}
nav>a:nth-child(2),nav>a:nth-child(4){
    color:#fb7403;
}
.menu{
    float: right;
}
.menu-list{
    display: none;
}
.menu-list li{
    color: #000;
}
.menu:hover .menu-list{
    display:block;
}
 
/* 小箭头 */
.arrow{
    float: right;
    width: 0;
    height: 0;
    border-style: solid;
    border-width: 20px 20px 20px 20px;
    border-color: #000 transparent transparent transparent;
}
 
 
.phone{
    position: absolute;
    right:0px;
    display: inline-block;
    width: 76px;
    height: 24px;
    margin: 0 atuo;
    background: url(../img/未标题-1.png) left  no-repeat;
    background-size:auto 100%;
    top:48px;
    text-indent: 24px;
}
 
/* 表单栏 */
.content{
    height: 800px;
    width: 1260px;
    background: #fff;
    position: relative;
    margin: 0 auto;
     
}
.content>h2{
    font-size:18px;
    line-height: 45px;
}
.content>h2>span{
    font-size:18px;
    color:#636363;
    font-weight: lighter;  
}
form{
    width:1256px;
    height: 630px;
    border:#fb7403 solid 2px;
    border-radius: 10px;
}
form>h2{
    font-size: 20px;
    line-height: 40px;
    background: #fb7403;
    border:#fb7403 solid 2px;
    border-radius: 5px;
    color:#fff;
    text-indent: 18px;
}
form>p{
    font-size: 14px;
    line-height: 20px;
    text-align: center;
    margin: 16px 0;
}
form>p:first-of-type{
    margin-top: 54px;
}
 
/* 设置各段文本长度，目的对其居中 */
form>p>span:nth-child(1){
    color: red;
    display: inline-block;
    width: 80px;
    text-align: right;
     
}
form>p>span:nth-child(2){
    display: inline-block;
    width: 70px;
    text-align: right;
     
}
form>p>span:last-child{
    display: inline-block;
    width: 390px;
    text-align: left;
}
form input,form select{
    display: inline-block;
    width: 210px;
}
/* 我已阅读并同意遵守 */
form>p:last-child{
    font-size: 20px;
    line-height: 20px;
}
input[type=checkbox]{
    width: auto;
}
/* 下一步 */
input[type=submit]{
    width: 230px;
    height:38px;
    color:#fff;
    background:#fb7403;
    border: none;
    border-radius: 5px;
    margin-top: 64px;
    margin-left: 413px;
}
/* 页脚 */
footer{
    color:#a19999;
    text-align: center;
    height: 100px;
    width: 100%;
    background: #dcdcdc;
    border-top:#2487c9 2px solid;
    padding-top: 20px;
     
}
footer>p{
    font-size: 16px;
    line-height:25px;
}