Stylewright

About

Make any website look the way you want. Stylewright is a clean, fast editor for writing your own CSS for any site — fix an eyesore, force
  dark mode, hide clutter, bump a tiny font, or completely restyle a page. Your changes are saved per site and waiting for you the next
  time you visit.

  WHY STYLEWRIGHT
  - Per-site memory. Open the side panel on any page and your last CSS for that exact site is already loaded — github.com keeps its look,
  separate from everywhere else.
  - A real editor. Write in a proper CodeMirror editor with CSS syntax highlighting and light/dark themes, right next to the page. Click
  Apply and see it live instantly.
  - You're in control. Nothing is applied automatically. Your CSS injects only when you click Apply — so it can never silently change a
  page behind your back.
  - Auto-apply when you want it. Like a site's look on every visit? Flip its "Apply automatically on page load" toggle. It's per-site and
  off by default — turn it off anytime.
  - Truly private. No account, no sign-in, no servers, no analytics, no tracking. Everything stays in your browser's local storage and
  nothing ever leaves your device. The build even ships a Content Security Policy that physically blocks the extension from making any
  network connection.
  - Minimal permissions. No scary "read and change all your data on all websites." It touches a page only when you click Apply, and asks
  for a single site's access only when you opt that site into auto-apply.
  - Yours to keep. Back up or move your styles with one-click JSON export/import. A global kill switch turns everything off at once.

  HOW IT WORKS
  1. Open the side panel on any site.
  2. Type or tweak your CSS (your saved styles are pre-loaded).
  3. Click Apply to see it live. Use Disable to stop applying while keeping your CSS, or Clear to empty the editor.

  Works in Chrome, Brave, and other Chromium browsers. Open source — built in the open.