PHP网站性能优化：如何减少HTTP请求以提高访问速度？

<?php
$css_files = ['style1.css', 'style2.css', 'style3.css'];

$combined_css = '';
foreach ($css_files as $file) {
    $combined_css .= file_get_contents($file);
}

file_put_contents('combined.css', $combined_css);
?>

<?php
$cached_file = 'cached.html';
$expiration_time = 3600; // 缓存时间为1小时

if (file_exists($cached_file) && time() - filemtime($cached_file) < $expiration_time) {
    // 使用缓存文件
    readfile($cached_file);
} else {
    // 生成新的HTML内容
    ob_start();
    // ... 生成HTML内容的代码 ...
    $html_content = ob_get_clean();
    
    // 写入缓存文件
    file_put_contents($cached_file, $html_content);
    
    // 输出HTML内容
    echo $html_content;
}
?>

.icon {
    background: url(sprite.png) no-repeat;
    width: 30px;
    height: 30px;
}

.icon-home {
    background-position: 0 0;
}

.icon-play {
    background-position: -30px 0;
}

.icon-setting {
    background-position: -60px 0;
}

.icon {
    background: url(data:image/png;base64,iVBORw0KG...) no-repeat;
    width: 30px;
    height: 30px;
}

<?php
$redirect_url = '';

if (condition1) {
    $redirect_url = 'redirect1.php';
} elseif (condition2) {
    $redirect_url = 'redirect2.php';
}

if ($redirect_url) {
    header('Location: ' . $redirect_url);
    exit;
}
?>