Style Engine Documentation

Installation

Install Style Engine from the Chrome Web Store, Microsoft Edge Add-ons or Firefox Add-ons, then pin it for quick access.

Quick start

1. Open a website and select the Style Engine icon.
2. Choose Global CSS, Global JS, Site CSS or Site JS.
3. Enable the rule and enter your CSS or JavaScript.
4. Changes are saved automatically by default.
5. When a website requires access, approve the browser permission request.
6. To use manual saving instead, disable Automatic save under Settings > Editor Behavior. Ctrl+S remains available for immediate saving.

/* example domain rule */
body {
  font-size: 16px !important;
  line-height: 1.6;
}

.promo-banner {
  display: none !important;
}

Core concepts

Global rules

Apply across supported websites while enabled. CSS and JavaScript can be enabled independently.

Site rules

Apply only to the selected domain. Each domain has independent CSS and JavaScript code and enable controls.

Automatic save

Editor changes are saved automatically by default. Automatic save can be disabled from Settings to restore manual Save controls.

Live CSS preview

CSS changes can be reflected on the active page while editing.

Live JavaScript preview

JavaScript preview is optional and can be disabled from Settings.

Clear

Removes the current editor content. With Automatic save enabled, the cleared state is saved automatically; otherwise save it manually.

How it works

Style Engine injects only the CSS and JavaScript entered by the user. Domain matching selects the applicable site rule set, while global and site rules remain independent.

CSS changes can be previewed live and Style Engine re-applies its CSS when required by dynamic page and SPA lifecycle changes.

Live JavaScript preview is optional. JavaScript rerun during SPA navigation is a separate setting and is disabled unless the user enables it.

Website source files are never modified and Style Engine does not download or execute remote code.

Backup and restore

Export the complete Style Engine configuration — settings, global rules and site rules — as a local JSON backup. Restoring a backup replaces the current configuration with the imported state. No cloud or browser-sync storage is involved.

Permissions

Website access is requested when a rule needs permission to run on a site.

Site-specific rules request access to the relevant website when required. Global functionality may require broader optional website access.

activeTab
storage
scripting
host permissions

Style Engine does not collect browsing history, transmit page content or execute remote code.

Troubleshooting

• Rules not applying: check the domain, enabled state and website permission.
• CSS has no visible effect: check the selector and CSS specificity. Website styles can still win through normal CSS cascade rules.
• JavaScript changes are not previewed while typing: confirm Live JavaScript Preview is enabled in Settings.
• JavaScript does not rerun after SPA navigation: enable Rerun JavaScript on navigation (SPA) under Settings > Editor Behavior.
• JavaScript not executing: check the browser console for syntax or runtime errors.
• Strict CSP or restricted browser pages: some pages can restrict extension script behavior or cannot be modified by browser extensions.

Privacy

Rules and settings remain in local browser storage. There is no tracking, analytics, remote code, external transmission of saved rules or browser sync storage for normal rule and settings persistence. Read the full policy