Loading html inside PHP for heroku - php

Question

I have created separate HTML and jquery sites for iPhone and Ipad. Cause I have used Heroku for deployment I have to have a PHP index. So I have included Html inside PHP. It loads the index.html inside there's folders.but the links are broken( CSS, Images ).
Is there any solution of alternative for that?
<?php
echo $width = "<script>document.write(screen.width);</script>";
echo $height = "<script>document.write(screen.height);</script>";
if($width!=null && height !=null) {
if($width>376 && $height>812){
include_once("ipad/index.html");
} else {
include_once("iphone/index.html");
}
} else {
echo json_encode(array('outcome'=>'error','error'=>"Couldn't redirect. Redirecting to iPhone version"));
}
?>
Note -
I have tried something like this
<?php
echo $width = "<script>document.write(screen.width);</script>";
// echo $height = "<script>document.write(screen.height);</script>";
if($width!=null) {
$path = $_SERVER['DOCUMENT_ROOT'];
if($width>376){
$path = $_SERVER['DOCUMENT_ROOT'];
$path .= "/StanstedGo/ipad/index.html";
include_once($path);
} else {
$path = $_SERVER['DOCUMENT_ROOT'];
$path .= "/StanstedGo/iphone/index.html";
include_once($path);
}
} else {
echo json_encode(array('outcome'=>'error','error'=>"Couldn't redirect. Redirecting to iPhone version"));
}
?>
but it also does not solve my problem. I still have broken links to CSS files.