> Code written for a web browser 30 years ago will still run in a web browser today.

Will it? - My browser doesn't have document.layers (Netscape) It seems to still have document.all (MSIE), but not sure it's 100% compatible to all the shenanigans from the pre-DOM times as it's now mapped to DOM elements.

The Space Jam website from 1996 still renders perfectly almost 30 years later.

https://www.spacejam.com/1996/

Those (document.layers and document.all) were both vendor-specific, neither were part of the w3c. I don't recommend ever writing vendor-specific code.

The w3c and standards have generally won so it's easier than ever to write to the standard.