I don't know if it's the done thing, but I've separated the CSS files into 'look' and 'feel'. One sets up the dimensions and whatnot, the other is responsible for colours and stuff. We'll see.
Rename database.php to utils.php as it's a general purpose utilities file now, not responsible for much database stuff at all really, thanks to PDO.
Change to include the new utils.php file instead of the old database.php file.
Search functionality taken out of the main index.html file and moved to its new home, search.js