Design does not exist in a vacuum. Technological progress, for example, creates the need for design change. Microsoft's switch from a serif to a sans serif font as the default typeface for Word was a good move, because we rarely print documents anymore and a the best design for print is not the same as the best design for screens.

20th century physics books had a distinct design for illustrations. It was beautiful and functional. But it was also designed around the limitations of their eventual monochrome (not even greyscale) print. A 2020 textbook does not have the same limitations and should not be designed with the same set of constraints.

That's one half. The other one is how people feel while using it. 1985 aesthetic makes people feel bad. Thus design is half bad. Or, for you maybe, half good.

Many would argue good fashion is timeless as well. A good chunk of haute couture from decades past would be seen as modern and appealing today. (Which is why the houses like to repackage and ship them as such...)

> Fashion is a popular aesthetic expression at a particular time, place and in a specific context, especially in clothing, footwear, lifestyle, accessories, makeup, hairstyle, and body proportions.

Fashion is inexplicably linked to a particular time. Just like Art - Art evolves with time and it is part of the culture, current events, etc.

Design is not (unless you want to include say media as it changes through time. For e.g. print -> digital media).

But not at every given point in time. That fashion ebbs and flows is a given, but that's not the same thing as being timeless.