Seldom websites’ style should be changed, since the identity of the owner and the message they want to give is built around it. Nevertheless, creative people often cannot help but being influenced by other websites’ design and graphical intuitions, so they are pushed to change, improve, tweak, experiment new appearances for their online creations.
For this reason, I believe it is very important to formerly develop and code a Permanent HTML structure, that is reasoning and thinking about a website HTML in order to keep it valid regardless of CSS changes.
In this way modifying little graphical things becomes easy and no class or tag ever needs to be changed, except for radical website rewrites, which change everything from the bottom to the top.
A turther improvement of Permanent HTML is
!Universal HTML