userstyles

userstyles are custom CSS themes that restyle websites right in your browser through managers like Stylus. I made a handful back when I was in high school (2020-2021) on userstyles.org to add dark modes to the sites I used daily.

In 2026 I came back to it to apply the latest AI agent capabilities (agentic workflows, autonomous loops, goal-driven runs) to a concrete task: AI agents running the whole flow end-to-end.

The agents work in distinct stages:

• Discovery: Scan for popular, high-traffic sites that have no native dark mode and either no userstyle at all or only broken/outdated ones (site redesigned, dead selectors, missing coverage), surfacing the most interesting opportunities.
• Build: Inspect the live site and author a complete dark theme, looping through multiple rounds of automated audits and self-review (zero white-surface leaks, WCAG contrast checks, sticky headers, dropdowns, charts, data tables...) to reach the best possible result.
• Packaging: Record a walkthrough video, capture promotional screenshots, and write the targeting rationale with all the metadata needed for publishing.

I keep the final step manual: I review the walkthrough and screenshots, then publish to userstyles.world and userstyles.org.
What makes it interesting is less the themes than the agent setup behind them: a real, end-to-end task handled autonomously, producing something people actually use: 50+ themes, 3500+ installs.