Quick start with plain HTML

Paste one module script into any HTML file. It loads the stylesheet and registers every component.

<script
  type="module"
  src="https://cdn.jsdelivr.net/npm/@pol-cova/gessi/dist/gessi.js"
></script>

<gessi-desktop menu="◆ My OS,File,View,Help" clock="09:41">
  <gessi-window title="hello.html" width="38rem" active draggable>
    <h1>One script, plain HTML</h1>
    <p>No package manager, bundler, or framework required.</p>
  </gessi-window>
</gessi-desktop>

02

Install from npm

Use the same CSS and native custom elements from a bundler or static-site layout.

Install

npm install @pol-cova/gessi

Import

import "@pol-cova/gessi/css";
import "@pol-cova/gessi/components";

Choose the entry point for your project

@pol-cova/gessiPackage default; component module

@pol-cova/gessi/cssStyles only; no registration

@pol-cova/gessi/componentsSSR-safe component registration

@pol-cova/gessi/gessi.jsCDN entry; loads sibling CSS

03

How do I…?

Start with the outcome you need. Each recipe is deliberately small enough to paste into a real project.

…apply a visual system?

Set data-gs-style on a page region, or use theme on a desktop environment.

Compare all five themes →

<main data-gs-style="retro">
  <article class="gs-card">…</article>
</main>

<gessi-desktop theme="classic-os">
  …
</gessi-desktop>

…open and close a dialog?

Keep the dialog in ordinary HTML, then call its small public API from a native button.

See window and dialog attributes →

<button id="open">Settings</button>
<gessi-dialog id="settings" title="Settings" hidden>
  <button>Done</button>
</gessi-dialog>

<script>
  const open = document.querySelector("#open");
  const dialog = document.querySelector("#settings");
  open.onclick = () => dialog.open();
  dialog.querySelector("button").onclick = () => dialog.close();
</script>

…add a non-destructive image effect?

Pass space-separated effects. Gessi composes them in the browser and leaves the source file unchanged.

Browse media effects →

<gessi-media
  src="/photo.jpg"
  alt="Night market"
  effect="chromatic grain scanlines"
  frame="polaroid"
></gessi-media>

…render Markdown as a Gessi post?

Wrap generated HTML in gessi-document or add class="gs-prose". No JavaScript or framework adapter is required.

Copy Markdown adapters →

<gessi-window title="notes.md" active>
  <gessi-document>
    <h1>Release notes</h1>
    <p>Rendered Markdown stays semantic.</p>
  </gessi-document>
</gessi-window>

…use Gessi in an SSR or static project?

Import CSS during the build and register components from a browser module. The component import is guarded for SSR.

Open framework recipes →

import "@pol-cova/gessi/css";
import "@pol-cova/gessi/components";

04

What can I build with Gessi?

Use Gessi when the interface benefits from recognizable places, tools, documents, media, or system chrome—not only for literal operating-system recreations.

Product

Launch pages that behave like software

Put product copy in a primary window, supporting proof in smaller windows, and navigation in the menu bar or dock.

Use: gessi-desktop gessi-window gessi-toolbar Open Product OS →

Portfolio

Personal sites and interactive archives

Represent projects as files, folders, documents, windows, or media objects while keeping every link and heading semantic.

Use: gessi-icons gessi-tree gessi-media Open the plain HTML start →

Application

Admin tools, control panels, and dashboards

Compose status panels, meters, lists, alerts, tabs, and dialogs without adopting a JavaScript framework runtime.

Use: gessi-panel gessi-meter gessi-dialog Open Classic OS →

Publishing

Blogs, release notes, and MDX essays

Drop generated Markdown into document styling, then frame it as a file, window, card, or plain article.

Use: gessi-document .gs-prose .gs-callout Open Markdown post →

Editorial

Media stories, maps, exhibits, and archives

Layer composable effects over source images, add accessible map markers, and present collections as a carousel.

Use: gessi-media gessi-map gessi-carousel Open Media OS →

Pattern: product page as a desktop

Use one dominant window for the primary narrative. Smaller windows should add context, not repeat the same content.

<gessi-desktop theme="neo">
  <gessi-window title="product.html" active zoomable>
    <main class="product-layout">
      <h1>Ship the work that matters.</h1>
      <p>Your product-specific content stays ordinary HTML.</p>
      <a class="gs-btn" href="/signup">Start free</a>
    </main>
  </gessi-window>
</gessi-desktop>

Pattern: compact settings tool

Let Gessi provide reusable chrome while labels, fields, and actions remain native controls.

<section data-gs-style="classic-os">
  <gessi-panel title="Preferences" columns="2">
    <label>Display name <input value="Ada"></label>
    <label>Theme
      <select><option>Classic OS</option></select>
    </label>
    <gessi-meter label="Storage" value="64"></gessi-meter>
    <button type="submit">Save changes</button>
  </gessi-panel>
</section>

Pattern: project gallery with effects

The effect belongs to presentation. Keep useful alt text and the original image asset.

<div class="project-grid" data-gs-style="retro">
  <gessi-media
    src="/work/archive.jpg"
    alt="Printed archive interface"
    effect="dither grain"
    caption="Archive, 2026"
    zoomable
  ></gessi-media>
</div>

05

Build with an AI coding agent

Gessi is AI-friendly because the output is still semantic HTML: a small set of named components, ordinary content elements, and explicit attributes instead of generated wrapper trees.

AI-native workflow, standards-native output

Replace the bracketed project details, paste it into your coding agent, and include a screenshot or product brief when you have one.

Names the exact package entry points.
Protects SSR, light DOM, semantics, and mobile flow.
Separates reusable Gessi chrome from project layout CSS.
Requires browser verification instead of code-only completion.

Agent prompt

You are implementing [PROJECT OR PAGE] using Gessi, a dependency-free CSS
and native Web Component library for expressive HTML.

Goal:
- Build [DESCRIBE THE INTERFACE AND PRIMARY USER TASK].
- Use the [neo | minimal | retro | old-tech | classic-os] visual system.
- Match [REFERENCE, BRAND, OR ART DIRECTION].

Integration:
- For plain HTML, load:
  <script type="module"
    src="https://cdn.jsdelivr.net/npm/@pol-cova/gessi/dist/gessi.js">
  </script>
- For a bundler, import "@pol-cova/gessi/css" and
  "@pol-cova/gessi/components".
- Do not add a framework runtime only to use Gessi.

Implementation rules:
- Use Gessi components for reusable interface chrome: desktop, windows,
  dialogs, menus, toolbars, docks, panels, alerts, media, maps, or carousels.
- Keep project content as semantic HTML: headings, links, buttons, lists,
  forms, images, and sections.
- Keep content in light DOM. Do not introduce Shadow DOM.
- Use native buttons for actions and native links for navigation.
- Put project-specific grids and content layout in ordinary scoped CSS.
- Do not invent one-purpose utility classes or wrap every element in a
  custom component.
- Keep imports safe during SSR and do not access browser globals at module
  evaluation time.
- Preserve keyboard access, visible focus, useful accessible names, alt text,
  long-content handling, and prefers-reduced-motion.
- At widths below 720px, convert positioned desktop UI into readable document
  flow without separate mobile markup.

Deliver:
1. The working implementation.
2. Any small scoped CSS needed for [PROJECT].
3. A short explanation of the chosen Gessi components.
4. Browser verification at desktop and mobile widths.

Before finishing, verify that the page has no horizontal overflow, clipped
content, console errors, inaccessible generic click targets, or unreadable
theme contrast.

06

Five visual systems, one HTML structure

Switch the style attribute. Components and semantic content remain unchanged.

New

Theme the same markup

Cards, controls, forms, and OS components share the selected visual language.

Project name

HTML CSS Web Components

Public custom theme tokens

Use data-gs-style="custom" or theme="custom", then set stable --gs-* tokens on the same element. These tokens are the supported customization surface for color, type, border, radius, shadows, focus, and window chrome.

--gs-inkPrimary text and foreground color

--gs-paperBase surface color

--gs-lineBorder and keyline color

--gs-blue --gs-mint --gs-tomato --gs-sunAccent palette

--gs-radius --gs-border-widthRadius and border scale

--gs-shadow --gs-shadow-smSurface and control elevation

--gs-window-bg --gs-window-title-bg --gs-window-body-bgDesktop window chrome

--gs-toolbar-bg --gs-control-bg --gs-control-textMenus, toolbars, and action controls

--gs-focusVisible focus outline

Custom theme

<gessi-desktop
  theme="custom"
  style="--gs-ink: #1b1026; --gs-paper: #fff7d6; --gs-line: #1b1026;
    --gs-window-title-bg: #ffd447; --gs-control-bg: #2ee6a6;"
>
  <gessi-window title="tokens.html" active>...</gessi-window>
</gessi-desktop>

Open the custom theme example →

07

CSS primitives

Use the class layer for normal pages, or combine it with the OS components.

.gs-cardContent surface

.gs-btnButtons and links

.gs-fieldInputs and selects

.gs-gridResponsive content grid

.gs-stackVertical rhythm

.gs-clusterInline control group

.gs-chipCompact metadata

.gs-proseRendered Markdown and long-form content

.gs-progressProgress indicator

08

Markdown and MDX content

Use gessi-document or .gs-prose around rendered Markdown. Headings, tables, code blocks, blockquotes, footnotes, task lists, callouts, and metadata are styled without JavaScript.

notes/post.mdJul 8, 20266 min read

Field Notes From a Tiny Desktop

Markdown output remains ordinary HTML, so links, lists, tables, and headings keep their native behavior.

Callout

Use .gs-callout for notes generated by Markdown plugins or hand-authored MDX.

Publish with semantic HTML.
Keep the content readable without JavaScript.

<article class="gs-prose">
  <h1>Post title</h1>
  <p class="gs-file-meta"><time datetime="2026-07-08">Jul 8, 2026</time></p>
  <p>Generated Markdown HTML goes here.</p>
</article>

export function BlogPost({ children, meta }) {
  return (
    <gessi-window title={`${meta.slug}.mdx`} active>
      <gessi-document>
        <p className="gs-file-meta">
          <time dateTime={meta.date}>{meta.date}</time>
          <span>{meta.readingTime}</span>
        </p>
        {children}
      </gessi-document>
    </gessi-window>
  );
}

---
import "@pol-cova/gessi/css";
const { Content, entry } = Astro.props;
---
<script>import "@pol-cova/gessi/components";</script>

<gessi-window title={`${entry.slug}.md`} active>
  <gessi-document>
    <p class="gs-file-meta">
      <time datetime={entry.data.date.toISOString()}>{entry.data.date.toDateString()}</time>
    </p>
    <Content />
  </gessi-document>
</gessi-window>

<article class="gs-prose">
  <p class="gs-file-meta">
    <time datetime="{{ page.date | htmlDateString }}">{{ page.date | readableDate }}</time>
    <span>{{ page.fileSlug }}.md</span>
  </p>
  {{ content | safe }}
</article>

<gessi-document>
  <p class="gs-file-meta">
    <time datetime="{{ .Date.Format "2006-01-02" }}">{{ .Date.Format "Jan 2, 2006" }}</time>
    <span>{{ .File.Path }}</span>
  </p>
  {{ .Content }}
</gessi-document>

Open the complete Markdown post example →

09

Desktop environments

Background patterns, semantic menus, icons, window stacking, and keyboard management are built in.

<gessi-desktop
  theme="classic-os"
  storage-key="product-desktop-v1"
  background="#c5c9ea"
  pattern="grid"
  pattern-color="#5a5f92"
>
  <nav slot="menu">
    <strong>⌘ Product OS</strong>
    <a href="/">File</a>
    <button type="button">Help</button>
  </nav>

  <gessi-window title="Projects" active draggable>
    Your normal HTML
  </gessi-window>
</gessi-desktop>

Persist layout

storage-key opts into localStorage persistence for position, size, layer, minimized, hidden, and active state. No storage access happens unless the attribute is present in the browser.

Layout methods

serializeLayout() returns JSON-safe state, restoreLayout(layout) applies trusted state, and resetLayout() clears the stored key.

Restore events

gs-layout-restore-before is cancelable. gs-layout-restore-after fires with the restored layout.

Local storage adapter

const desktop = document.querySelector("gessi-desktop");
const key = "my-desktop-layout";

desktop.restoreLayout(localStorage.getItem(key));
desktop.addEventListener("gs-layout-change", () => {
  localStorage.setItem(key, JSON.stringify(desktop.serializeLayout()));
});

10

Windows and dialogs

Generated chrome, draggable positioning, nested child windows, focus stacking, controls, slots, and dialog focus management.

`<gessi-window>`

title x y width height draggable minimizable zoomable

Content slots

toolbar sidebar status

`<gessi-dialog>`

open() and close(), Escape handling, focus trapping, and focus restoration.

11

Navigation and OS shell

Small semantic components replace large stacks of utility classes.

gessi-menuKeyboard-aware native link and button menu

gessi-toolbarScrollable command bar

gessi-dockTop, bottom, left, or right application dock

gessi-breadcrumbResponsive location trail

gessi-tabsTheme-aware tab row

gessi-treeNested file and navigation structure

12

System UI components

Build control panels, status surfaces, notifications, and file-like interfaces out of the box.

12 files were prepared.

13

Composable image effects

Stack effect names without changing the original file or shipping an image-processing dependency.

<gessi-media
  src="/photo.jpg"
  alt="Night market"
  effect="chromatic grain scanlines"
  frame="polaroid"
  aspect="4 / 3"
  zoomable
></gessi-media>

14

Maps and markers

Use a real image or inline SVG, then place accessible percentage-based markers above it.

SF

LDN

TYO

15

Carousel

Every direct child becomes a keyboard-accessible slide with generated themed controls.

<gessi-carousel aria-label="Featured work" autoplay="5000">
  <article>First story</article>
  <article>Second story</article>
  <article>Third story</article>
</gessi-carousel>

16

Responsive by default

Below 720px, desktop composition becomes readable document flow without separate mobile markup.

Positioned windows and child windows return to document flow.
Toolbars and docks scroll horizontally instead of compressing controls.
Sidebars collapse while primary content remains visible.
Media, maps, carousels, menus, and content grids remain fluid.

17

Static framework recipes

Native custom elements work in Astro, Eleventy, Hugo, Jekyll, server templates, and framework applications.

<script type="module"
  src="https://cdn.jsdelivr.net/npm/@pol-cova/gessi/dist/gessi.js">
</script>

---
import "@pol-cova/gessi/css";
---
<script>
  import "@pol-cova/gessi/components";
</script>

node_modules/@pol-cova/gessi/dist/gessi.css
node_modules/@pol-cova/gessi/dist/gessi.js

18

Keyboard controls

Desktop interactions include keyboard window management and accessible dialog behavior.

F6Cycle windows

Shift + F6Cycle backward

Ctrl + Shift + ArrowMove active window

EscapeClose dialog or popup menu

19

Complete environments

Open the examples, inspect the source, and use them as starting points.

Product OSLanding page as a desktop

Classic OSMonochrome control panels

Media OSEffects, map, carousel, and nested windows