Show HN: X86CSS – An x86 CPU emulator written in CSS

[Dylan16807]

> A hover-based clock, such as the one in Jane Ori's CPU Hack, is fast and stable, but requires you to hold your mouse on the screen, which some people claim does not count as turing complete for whatever reason, so I wanted this demo to be fully functional with zero user input.

That hover clock post is from 2023 and the "some people claim does not count" post is 2022. They were probably talking about the ones that make you check thousands of boxes to drive the logic forward.

Anyway, very cool advancement.

[rebane2001]

I wasn't sure whether to address the disconnect in the FAQ - I wanted it to be short and readable.

The idea is that, since a long time ago, there has always been demos that prove turing completeness and other programmy qualities in CSS, but that which people dismiss as requiring user inputs. The ones around by the time the comment got made were definitely at the "keep on clicking on the same spot on the screen" level - essentially just providing a clock.

And seeing discussion from after Jane Ori's hack, many still claim that even as much as hovering your mouse on a specific part of the screen makes css not a programming language.

[mbreese]

This is a cool demo, but it tells me that CSS might be too complex now. Why should you be able to emulate a CPU with a styling language? I’m not sure what you get by using a Turing complete language for visual styling.

[FartyMcFarter]

I don't know much about CSS, but Turing completeness is notorious for showing up in systems unintentionally.

It doesn't take much to be Turing-complete - if a system provides unbounded read/write memory plus branching or conditional recursion you're usually there.

As an example, Magic The Gathering (the card game) is Turing-complete: https://arxiv.org/abs/1904.09828 . You can use creature tokens as memory and various game mechanics to do flow control. Was this intentional by the designers? Most likely not...

[namuol]

Less JavaScript is a bad thing now?

[dmitrygr]

There is absolutely no reason for css to be turing complete. None. That being said, well done

[notepad0x90]

Can an argument be bade that CSS only exists becuase javascript failed to develop a styling component to displace it?

I like to think webassembly is the right track. But ECMAScript and CSS alike need(ed) to devolve into a simpler byte-code like intermediary language syntax.

Browsers supporting complex languages has always been a bad idea, what they need to support is capabilities, and access and security primitives. wasm hasn't displaced javascript, because afaik, the wasm spec for browsers doesn't require them to implement javascript (and ideally, CSS) via wasm.

Instead of distilling, simplifying and speccing CSS and Javascript, browsers caked on layers upon layers of complicated features. The idea that browsers should define and regulate the languages developers use to write front-end code needs to die.

[senfiaj]

I have mixed feelings. On the one hand, it's impressive, but on the other, it's concerning that CSS is turning into "JavaScript 2".

[0x7cfe]

Now we can embed a cryptominer on a page even with JS disabled! /s

[notpushkin]

Whoa!

Completely unrelated but somehow unsurprising:

Zero-day CSS: CVE-2026-2441 exists in the wild - https://news.ycombinator.com/item?id=47062748 - February 2026 (233 comments)

[rebane2001]

I do actually have a CSS CVE[0] in Chrome, but it was in the changelog as "in Animation" instead of "in CSS", so no fun stories/headlines for me :c

[0] https://chromereleases.googleblog.com/2025/06/stable-channel...

[magicalist]

That was in the C++ implementation of the CSS interface that gets exposed to JS, though, there wasn't an exploit from CSS.

[carra]

I don't think it's that unrelated. If you make a system way more complex than it should be (clearly the case with CSS) it's obvious the risk of vulnerabilities increases exponentially.

[btdmaster]

Very cool. The horsle demo made me think, how hard would it be to add a virtual memory address (or a non-8086 RAND instruction) that returns a random byte (that would allow it to pick a random value and get a standard wordle working in principle)

I see CSS random() is only supported by Safari, I wonder if there's some side channel that would work in Chrome specifically? (I guess timing the user input would work)

[rebane2001]

It's really easy, I was considering adding it.

The easiest way is to make an @property that's animated at ridiculous speeds that can be sampled to get (sort of) random bits.

[RedShift1]

Definitely in the "they didn't stop to think if they should" category.

[sgjohnson]

They probably did, and just determined that it would be fun.

The other week I had a fun project to implement IPv6 support in TempleOS. I did stop to think whether I should, and determined that absolutely not.

I asked Claude to start planning on doing it. It started referencing ZealOS, which is a fork of TempleOS and already has a functioning TCP stack.

That's when I determined that it would no longer even be fun, because someone else had already done all the heavy lifting, and gave up.

[BirAdam]

I know everyone is saying "CSS doesn't need to be Turing complete" but... to me, this just shows the JS isn't needed anymore.

[freakynit]

Incredible achievement. Horrible development on CSS front.

CSS should NOT be becoming turing complete. Nor any other DSL.

[mspreij]

> CSS should NOT be becoming turing complete. Nor any other DSL

Hasn't it been so for a while? I mean I agree with you but it's a bit late

[pjmlp]

That is the problem though, DSLs always end up becoming turing complete, because there is always that use case they don't cover.

[csmantle]

I think we can look forward to running this on more non-Chrome browsers once @function [0] gets wider support?

[0]: https://caniuse.com/wf-function

[rebane2001]

It relies on a few things, but @functions, if() statements, and container style queries are the main ones.

[ebolyen]

The moxy of this is inspiring.

I'm curious to know what you would rate as the most important features to make this work? It seems like calc+if do a lot of the heavy lifting, but the new function syntax is what makes instruction lookup tractable.

[andrewstuart]

Abomination! (Makes sign of cross)

Also: wow.

[namuol]

Predictably, all the same people who bemoan JS ubiquity feel the need to express their distaste for advances in CSS in this thread. Nobody is actually doing stuff like this in real applications, it’s just a demo, for fun.

I get the feeling some people just hate the web.

[Dylan16807]

Your grumpiness contradicts itself. To the extent that it's just for fun, it's not an advance.

And CSS being Turing complete doesn't make it suitable to replace any JS it couldn't already replace, so why can't JS-haters dislike the idea? If I didn't like a language and people offered an even worse to use replacement I'd be justified in having distaste for it!

[hudecekdev]

This is absolutely horrible... in a good way. Kinda like Doom in a PDF. Well done.

[voidUpdate]

So is this x86 compatible, or 8086 compatible? Because those are different things

[rebane2001]

8086 is x86

https://en.wikipedia.org/wiki/X86

[bux93]

There's a list of the supported opcodes on the page if you scroll down.

[sunbum]

If it was 8086 they would have written 8086

[randfur]

Really looking forward to a how it works post. What is that READMEM_1??

[rebane2001]

it's a placeholder that gets replaces by the python script on build

[Aloha]

This feels like... just because you can, doesnt mean you should.

[MetaMonk]

this is incredible

[warpspin]

Next step: Start Chrome in emulated X86CSS and start X86CSS in emulated Chrome.

[nottorp]

Next logical step is to compile the CSS to webassembly, of course!

[_s_a_m_]

Only Chrome ..

[NoiseBert69]

Bruh...

Can it mine bitcoins or run worms?

[desdenova]

[flagged]

[gurjeet]

> Your browser is unable to run this demo. Please try with an up-to-date Chromium-based browser.

Sorry to see internet regressing to Internet Explorer days.

Edited to add: This is the message I get when using Firefox.

[randfur]

For what it's worth Firefox has a bug open to implement some of the core CSS features being used here: https://bugzilla.mozilla.org/show_bug.cgi?id=1950366

[StilesCrisis]

Not really, Internet Explorer was single platform and closed source.

[rebane2001]

i'm glad llms won't be coming after my niche anytime soon

[nsonha]

I realy hope an AI did this intead of human, such a waste of time (the css part, not the x86)

[marmakoide]

Don't look at the end destination, look at the journey to the destination

* Learn low-level details of a basic but real-world CPU

* Practice the brain gymnastic of programming an atypical Turing-complete computer

Your created new connections in your brain, put to use some of the old established connections. Having a machine spit-out the emulator would rob you of all that. Like, you can drive from A to B, but running for A to B can do you much good.

[saagarjha]

This seems like a great use of time actually

[rebane2001]

I did not use any AI

[sakesun]

If an AI can do this, it's definitely an AGI.