HTML looks like this:
<!DOCTYPE html> <html> <head> <title>Gravity 1</title> <script src="./gravity1.js" async></script> <meta charset="utf-8"/> </head> <body> <canvas id="canvas" tabindex="" width="1000" height="800"></canvas> </body> </html>
CSS is used to make webpages look nicer. Ignore it for now.
This website is hosted on Neocities. You can go to https://neocities.org/ to create a website for free.
Flash is going to die, but it looks like Scratch 3.0 will not depend on Flash and that "a public alpha release is planned for the first quarter of 2018".