How can i write url specific CSS
you can use the following, it implements drupal_add_css().

if($_GET['q']=="user/23/prayerrequests") {
  drupal_add_css(path_to_theme() . '/custom_stylesheet.css', 'theme', 'all');
}


Edit 1:
If you want this to be able to do it for all users, you could use me aliases module. It enables you to use me in place of %uid.
So, the code would become

// "me" from the code is automatically replaced by uid of current logged in user.
if($_GET['q']=="user/me/prayerrequests") {
  drupal_add_css(path_to_theme() . '/custom_stylesheet.css', 'theme', 'all');
}


Edit 2:
You can use the variable global $user in the above code. You'll not need to install me aliases module.

//replace THEME with your theme name
function THEME_preprocess_page(&amp;$variables) {
  global $user;
  if($user-&gt;uid == 0) {
    return;
  }
  elseif ($_GET['q']=="user/".$user-&gt;uid."/prayerrequests") {
    drupal_add_css(path_to_theme() . '/custom_stylesheet.css', 'theme', 'all');
}


Don't forget to clear the caches.