Enterprising developer somehow writes an x86 CPU emulator in plain CSS — no Javascript, no WASM, just stylesheet computing
Source: Tom’s Hardware
Image credit: Getty
Lyra Rebane, a developer who blends CSS tricks with infosec knowledge, discovered that modern browsers’ stylesheet engines are powerful enough to emulate an x86 processor using only CSS—no JavaScript, WebAssembly, or other scripting. The project can be explored live at the x86 CSS emulator page.
Capabilities and Limitations
- The emulator implements most of the x86 instruction set, but it lacks key features such as interrupt handling, port I/O, and block‑operation instructions.
- Because of these gaps, it cannot yet run complex software like Doom, which requires a 32‑bit CPU (80386+), 4 MiB of RAM, and protected‑mode support.
Development Background
- Rebane built the emulator without any AI assistance or “vibe‑coding.” She notes that the logical leaps needed to turn CSS into a full‑featured state machine demand creative, out‑of‑the‑box thinking.
- She cites Jane Ori’s CSS CPU Hack as a key inspiration for her approach.
“I built an entire x86 CPU emulator in CSS (no JavaScript). You can write programs in C, compile them to x86 machine code with GCC, and run them inside CSS.” – Lyra Rebane
Tweet with demo (February 24 2026)
Purpose and Reception
Rebane describes the project as purely for fun. While many developers joke about HTML and CSS being “programming languages,” this work demonstrates that, with enough ingenuity, CSS can be pushed far beyond its intended styling role. Some readers have speculated about CSS becoming a serious attack vector, but the effort required to build such a processor suggests that this is unlikely in practice.
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