无法加载某些页面html或css

我正在为大学做一个数据库项目，但实际上我的问题与html或css有关（我想）。

事情是这样的：我在网站周围有一个导航栏，但当我在某些页面上时，我无法访问其他页面，例如，当我在"更改密码"页面上，并将鼠标放在"注销"上时，就无法点击。

提前感谢，André

这是代码：

<div id="linking">      
    <ul>
        <li>
            <a href="index.php">Home</a>
        </li>
        <li>
            <a href="trips.php">Search for trips</a>
        </li>
        <?php
        if (isset($_SESSION['user_logged_in'])) {
            if (($_SESSION['user_email']) === "admin@email.com") {
                ?>
                <li>
                    <a href="new_tour.php">Create tour</a>
                </li>
                <li>
                    <a href="new_service.php">Create service</a>
                </li>
                <?php
            }
            ?>
            <li>
                <a href='profile.php'>Change settings</a>
            </li> 
            <li>
                <a href='change_password.php'>Change password</a>
            </li>                       
            <li>
                <a href='logout.php'>Log out</a>
            </li>
            <label>Hello <?php print_r($_SESSION['user_name']) ?>!</label>
            <?php
        } 
        else {
            ?>
            <li>
                <a href='login.php'>Log In</a>
            </li>
            <li>
                <a href="new_customer.php">Register</a>
            </li>
            <label>Hello visitor!</label>
            <?php
        }
        ?> 
    </ul>
</div>

这是css：

/* common properties */
body{
    background-color: #d8d8d8;
}
hr{
    color: firebrick;
    background-color: firebrick;
    border-color: transparent;
}
.registering {
    position: absolute;
    left: 30%;
    top: 0%;
}
.loging {
    position: absolute;
    left: 33%;
    top: 25%;
}
td{
    vertical-align: middle;
}
/* .loging class properties */
body .loging{  
    position:absolute;
    left:32%;
    top:25%;
}
.loging td{
    padding:  5px;
    text-align: center;
    font-size: 20px;
    font-family: sans-serif;
    color: firebrick;
}
.loging td input{
    width: 500px;
    height: 23px;
    border-bottom-right-radius: 10px;
    border-top-left-radius: 10px;
    border-style: solid;
    border-color: transparent;
    text-align: center; 
    font-size: 16px;
}
.loging td input[type="submit"]{
    width: 120px;
    height: 30px;
    background-color: firebrick;
    color: #FFFFFF;
    font-size: 18px;
    font-weight: bold;
    border-radius: 0px;    
}
.loging td input[type="password"]{
    font-size: 24px;
}

/*. registering class properties */
.registering td{
    padding: 5px;
    text-align: center;
    font-size: 18px;
    font-family: sans-serif;
    color: firebrick;
}
.registering td input{
    width: 500px;
    height: 23px;
    border-bottom-right-radius: 10px;
    border-top-left-radius: 10px;
    border-style: solid;
    border-color: transparent;
    text-align: center; 
    font-size: 16px;
}
.registering td input[type="submit"]{
    width: 120px;
    height: 30px;
    background-color: firebrick;
    color: #FFFFFF;
    font-size: 18px;
    font-weight: bold;
    border-radius: 0px;
}
.registering td input[type="password"]{
    font-size: 24px;
}
/* .linking properties */
#linking label{
    color: firebrick;
    font-weight: bold;
    float:right;
    position: fixed;
    left: 90%;
    font-family: sans-serif;
    font-size: 16px;
}
li{
    display: inline;
    padding-right: 2px;
    padding-left: 2px;
}
a{
    color:firebrick;
    font-weight: bold;
    position: relative;
    display: inline-block;
    font-family: sans-serif;
    font-size: 14px;
    text-decoration: none;
}

/* section properties */
section{
    padding:5px;
    position: absolute;
    width:30%;
}
section table{
    padding: 8px;    
}
section hr{
    background-color: #FFFFFF; 
}
section td, th{
    width:32%;
    text-align: center; 
}

/* search for trips */
body .search{  
    position:absolute;
    left:32%;
    top:25%;
}
.search td{
    padding:  5px;
    text-align: center;
    font-size: 20px;
    font-family: sans-serif;
    color: firebrick;
}
.search td input{
    width: 500px;
    height: 23px;
    border-bottom-right-radius: 10px;
    border-top-left-radius: 10px;
    border-style: solid;
    border-color: transparent;
    text-align: center; 
    font-size: 16px;
}
.search td input[type="submit"]{
    width: 120px;
    height: 30px;
    background-color: firebrick;
    color: #FFFFFF;
    font-size: 18px;
    font-weight: bold;
    border-radius: 0px;
}

Logout.php代码：

<?php
session_start();
unset($_SESSION['user_logged_in']);   
session_destroy();
header("Location:index.php");
echo "<script>alert('You have been logged out! Please come back anytime!')</script>";
?>