导航栏不对字体显示不出

代码中的字体颜色设置成白色，为什么不会再导航栏显示，另外请老师帮忙看一下代码有哪些改进之处，O(∩_∩)O谢谢

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

<!DOCTYPE html>
<html>
<head>
 <meta charset="UTF-8">
 <title>3-3编程题</title>
 <style type="text/css">
  *{
   margin:0;
   padding:0;
  }
  body{
   min-width: 1000px;
  }
  .header{
   float:left;
   width: 100%;
   background-color: black;
   height:100px;
   line-height: 100px;
   /*为什么我这里不设置字体颜色会显示不出字体？*/
   color:white;   
   position: fixed;
   z-index: 99999;/*使导航栏显示在内容上方*/
   top:0px;
  }
   div.header img{float: left;}
   div.header p{
    float: right;
   }
     div.header p span{
      cursor:pointer;
     }
     div.header p span:hover{
      color: orange;
     }
  .footer{
   float:left;
   width: 100%;
   background-color: black;
   height:50px;
   text-align: center;
   line-height:50px;
   color:white;
   position: fixed;
   bottom: 0;
  }
  div.footer p span{
   cursor: pointer;
  }
  /*圣杯布局*/
  .container{
   padding: 100px 250px 0 350px;   /*加入100px上内边距，使文字不被遮盖*/
  }
  /*圣杯布局核心*/
  .left,.right,.middle{
   position: relative;
   float: left;
   min-height:1000px;
   padding-top: 100px;
  }
  .middle{
   width: 100%;
   background-color: #ffc0cb;
   text-align: center;
  }
  .left{
   width: 350px;
   background-color:#ffefdb; 
   margin-left: -100%;
   left:-350px;
  }
  .right{
   width: 250px;
   background-color: #add8e6;
   margin-left: -250px;
   right:-250px;
  }
  /*内容样式处理*/
  div.left table{
    width: 100%;
    float: right;
    position:absolute;
    top:100px;
  }
  div.left table td{
   margin: 10px;
   padding: 10px;
     }
  div.left table tr td span{
    background-color:#f06; 
   }
  .denglu{
   width: 100%;
   float: left;
   padding-left:10px;
   position:absolute;
   top: 100px;
  }
  h2{
   margin-bottom: 10px;
  }
  .form{
    width:200px;
               height:30px;
               margin-top:10px;
                margin-bottom:10px;
                font-size:10px; 
                border-style: none;
  }
  .submit{
   width:200px;
               height:35px;
               margin-top:10px;
                margin-bottom:10px;
               background-color:#ff0002;
               color:#fff;
               font-size: 14px;
               border-style: none;  }
 </style>
</head>
<body>
 <div class="header">
  <img src="logo.png">
  <p><span>课程</span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span>职业路径</span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span>实战</span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span>猿问</span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span>手记</span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</p>
 </div>
 <!-- 这是页面的内容 -->
 <div class="container">
  <div class="middle">     <img src="6.jpg">
    
  </div>
  <div class="left">      <table>
         <tr><td><h2>课程推荐</h2></td></tr>
      <tr><td><span>职业路径</span>&nbsp;&nbsp;&nbsp;&nbsp;HTML5与CSS3实现动态网页</td></tr>
      <tr><td><span>职业路径</span>&nbsp;&nbsp;&nbsp;&nbsp;零基础入门Android语法与界面</td></tr>
      <tr><td><span>职业路径</span>&nbsp;&nbsp;&nbsp;&nbsp;iOS5基础语法与常用控件</td></tr>
      <tr><td><span>职业路径</span>&nbsp;&nbsp;&nbsp;&nbsp;PHP入门开发</td></tr>
      <tr><td><span>职业路径</span>&nbsp;&nbsp;&nbsp;&nbsp;Java入门开发</td></tr>
     </table>   </div>
  <div class="right">
     <div class="denglu">
       <h1>登录</h1>
            <form>
                 <input type="text" name="username" placeholder="请输入登录邮箱/手机号" class="form"><br>
                 <input type="password" name="password" placeholder="6-16位密码，区分大小写，不能用空格" minlength="6" maxlength="16" class="form"><br>
                 <input type="submit" name="submit" value="提交" class="submit">
            </form>
     </div>
  </div>
 </div>
 <div class="footer">
 <p><span>网站首页</span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span>企业合作</span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span>人才招聘</span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span>联系我们</span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span>常见问题</span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span>友情链接</span></p>
 </div>
</body>
</html>