PHP: 无法引用css文件？-PHP中文网问答

最近学PHP，到第三章的时候卡住了。我引用了一个HTML模板，但是这个模板无法引用css文件，下图是这个HTML模板：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title><?php echo $page_title; ?></title>    
    <link rel="stylesheet" href="../ch03/includes/style.css" type="text/css" media="screen" />
    <meta http-equiv="content-type" content="text/html; charset=utf-8" />
</head>
<body>
    <p id="header">
        <h1>Your Website</h1>
        <h2>catchy slogan...</h2>
    </p>
    <p id="navigation">
        <ul>
            <li><a href="index.php">Home Page</a></li>
            <li><a href="calculator.php">Calculator</a></li>
            <li><a href="#">link three</a></li>
            <li><a href="#">link four</a></li>
            <li><a href="#">link five</a></li>
        </ul>
    </p>
    <p id="content"><!-- Start of the page-specific content. -->
<!-- Script 3.2 - header.html -->

但是，我通过在位于表头中的<style>标签里加入:

<?php include ('./includes/style.css'); ?>

它又工作了。通过审查源代码发现所有CSS代码都集中到这个HTML文件来了。我知道这样不好，但有没有办法解决？

还有，我在网站根目录里放入 *.html 文件提示 File not found.（能解析*.php）。

Nginx配置文件：

server {
    listen 80 default_server;
    root /var/www/html;
    index index.html index.php;

    charset utf-8;

    location / {
        try_files $uri $uri/ /index.php?$query_string;
    }

    location = /favicon.ico { access_log off; log_not_found off; }
    location = /robots.txt  { access_log off; log_not_found off; }

    access_log off;
    error_log  /var/log/nginx/error.log error;

    sendfile off;

    client_max_body_size 100m;

    location ~ \.php$ {
        fastcgi_split_path_info ^(.+\.php)(/.+)$;
        fastcgi_pass php:9000;
        fastcgi_index index.php;
        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        fastcgi_intercept_errors off;
        fastcgi_buffer_size 16k;
        fastcgi_buffers 4 16k;
    }

    location ~ /\.ht {
        deny all;
    }
}

=====================UPDATE on 2016.02.16 00:56===================

这是修改后的代码：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title><?php echo $page_title; ?></title>    
    <meta http-equiv="content-type" content="text/html; charset=utf-8" />
    <style>
    <?php include ('./includes/style.css'); ?>
    </style>
    <!-- <link rel="stylesheet" href="../ch03/includes/style.css" type="text/css" media="screen" /> -->
</head>

对，它能工作：