Almost everything looked like this in the 90s:

https://en.wikipedia.org/wiki/Jazz_(design)

Vaporwave is that

It would be this.

Doc Martens and flannel. Can you smell the grunge?

I've sometimes seen the style attributed to the "Memphis Group," but I don't know enough about design history to flesh that out, confirm, etc. Example photo of some of their items from the Wiki:

It'd be Niravana done in the style of Phil Collins while the video shows a vhs recording of people partying on a beach in board shorts and bikinis flanked by skaters in JNCO jeans with POGs glued to their skateboards with a club in the background that's called "The Edge", which is brightly adorned with a combination of "that cup design" and the pastel RGBY in geometric shapes while inside its actually got a simultaneous jungle and future aesthetic.

It's kind of earlier, but a little bit would be casette futurism.

https://tvtropes.org/pmwiki/pmwiki.php/Main/CassetteFuturism

A technological aesthetic reminiscent of mid-1970s to late 1990s tech (regardless of the real-time setting of the media) as codified by early microcomputers like the Altair 8800 and the IBM Personal Computer, late Cold War era technology, the iconic imagery of the mid to late space race, or the post-Cold War "end of history" period in The '90s, which was characterized by a fascination with virtual reality technologies (such as helmets) and 2D computer animation.

Whether it be the bold colors and geometric shapes, the tendency towards stark plainness, or the exotic-looking computers and proto-cell phones, it is clear that this is neither the Raygun Gothic of days past nor the Everything Is an iPod in the Future aesthetic that would follow, but a bridging point that contains elements of both styles.

Amazingly, nobody appears to have done a Wikipedia page for cassette futurism yet, or I'd link to that.

EDIT: Here's a DDG link to an image search for cassette futurism, to sort of give an idea:

https://duckduckgo.com/?t=h_&q=cassette+futurism&iax=images&ia=images

Depends on which part of the 90s. That whole “deep space nine” color palette was huge in the early 90s — lots of maroons and mustards and dark grays.

A return to innocence, a return to ..Enya!

I've got a fun option for where to start, windows media player skins

Most of this was the 2000s but what's a little bit of misdating

The same way 90s kids learned to dress like earlier generations. We learned it from the movies and TV reruns. We learned to dress like 50s greasers from Grease. We got our 60s and 70s hippy fashion sense from Cheech and Chong.

Grungy Hacker chic: See movies like Hackers (duh), Strange Days, The Matrix, Fight Club, The Crow, Blade, The Fifth Element, Tank Girl, etc. Tight fits. (You can spot the squares in this aesthetic by their baggy tracksuit fits). Lots of dark and dirty retro futurism stuff. Deliberate splashes of vibrant colors if anything other than black. Lots of strange materials you wouldn't normally consider clothing. Did they literally pick that accessory out of the trash? Maybe. Eyeliner on everyone, even the boys, especially the sad boys. Big black boots.

For more normal stuff, see the fashions in Weekend at Bernies, Wayne's World, Airheads, Bill and Ted's Excellent and Bogus Journeys, Go, Mallrats, Chasing Amy, Clerks, Friday, Point Break, My Cousin Vinny, White Men Can't Jump, Bad Boys, Clueless, Empire Records, etc. Lots of baggy fits. Lots of flannel, usually layered over a T-shirt. Ripped Jeans. Mostly muted subdue colors, with occasional splashes of virbancy, like a loud tie on a brown suit. Big and often long hair on the boys (and no beards). Sneakers. Tracksuits. Typing this out, these styles seem way too real and not all that exaggerated.

And then very briefly, there was a flash of retro swing revival and everyone wanted to dress like Jim Carey in The Mask.

I guess younger imitators might try to throw all these styles in a blender and see what comes out. Flannel Goths. Bubblegum Neon Hackers. Zoot Track Suits. Ripped Jeans and literally garbage. No clothes at all, just rocking boots and their cyber deck/stim-suit like a princess from Mars as written by William Gibson.

Surfers wearing bright pastels, talking like ninja turtles, all shot on cheap video cameras.

The movie Hackers.

Dockers pale brown/green, wool, plaid.

I don't rightfully know, but my heart says "The hotwheels logo"

I don't know everything that would end up in it, but DayGlo shit would definitely be one of them.

Hell, the image of a stereotypical zoomer already looks like they are harkening back to the 90's aesthetic.

Synthwave was the result of taking futurist stuff from the 1980s, and then decades in the future creating a nostalgic 1980s retrofuturism-themed theme combining various things like Tron and Outrun.

So I guess that the closest analog would be looking for aesthetics from movies that were aiming for a futuristic vibe in the 1990s, then combining those.

https://old.reddit.com/r/scifi/comments/1bauod1/in_retrospect_1990s_scifi_film_had_a_very/

In retrospect, 1990s sci-fi (film) had a very distinct style.

At the time you couldn't really tell, but looking back at the body of work that came out during that time, there was a very distinct style...and that style was apparently rust, lots of tubes connecting everything and up close shots with a fish eye lens.

Spaceship? Make it as rusty and dark as possible.

Medical scene? Connect her to 75 tubes to nowhere.

Getting chased down a corridor? Fish eye, baby.

I swear this is like every other sci fi film from 94 until 2000. A lot of it is almost reminiscent of horror.

70's sci fi was still the era of tin foil and white jumpsuits. (Logans Run, Zardoz, etc. Star Wars was the exception, not the rule.) 80's sci fi was darker and grittier and more serious looking drama, heavily influenced by Star Wars and Alien at the end of the 70's. (TWOK, Blade Runner, Aliens, etc.) A lot of that mid-late 90's stuff was leaning into horror, and kind of continuing a trend of the 80's darker sci fi popularity. Then by like 2009, you had the Apple Store aesthetic in the Star Trek reboot where the style was "the future's so bright you gotta wear shades." It was all lens flares for a few minutes.

So I guess maybe it'd have more of a horror vibe than synthwave?

The 90s was Pop Art

Nu-metal buttrock played by white guys dressed like cholos.

90s enjoyers have been just doin their thing all along

Depends on a couple things. 90's then or what we think of the 90's now?

Also, first half or second half. Because basically, the internet. The internet really wasn't a thing in peoples homes for the first half of the 90's. That became a thing starting around 95, and became pretty much ubiquitous by the year 2000.

The early 90's were basically the 80s. The later half was like, grunge, pop-punk, early internet.

It's The Matrix

It’s only denim.

Whatever it is it involves zumba pants