Is HTML, CSS, and JS executed on client side?

HTML, CSS and JS actually is executed on client side. The reason it is in your PHP file, is we need some way of delivering the code to the client. It doesn’t just magically appear. CSS and JS doesn’t even have to be in the PHP file. You can use HTML inclusions to let the browser fetch it eg.
For More Information Please Refer:
You May Also Like to Read: