<!DOCTYPE html> <html lang="en" > <head> <meta charset="UTF-8"> <title>Background fade demo</title> <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/meyer-reset/2.0/reset.min.css"> <link rel="stylesheet" href="./style.css"> </head> <body> <div class="past"></div> <div class="present" id="present"></div> <button id="toggle">Toggle</button> <script src="./script.js"></script> </body> </html>