jimit105/markdown-renderer ? reverse-engineered prompt

Build me a free Markdown editor that runs entirely in the browser with no sign in, no server, and no build step. I want to type Markdown on one side and see a live preview on the other side as I write, with GitHub style Markdown support like tables, task lists, strikethrough, code blocks, links, images, and blockquotes.

Please add syntax highlighting for code snippets and support Mermaid diagrams too. I want a dark mode toggle that follows my system setting and remembers my choice. On desktop it should show editor and preview side by side, and on mobile it should stack nicely. It would be great if I can drag the divider to resize the two panels.

Also add a share button that turns the current document into a link I can copy and send to someone else so they see the same content. Make it simple, fast, and polished, and if you need current docs for the libraries or browser behavior, look them up online.