Prompt

Make an app that shows colour palettes. It has to be a single HTML file that opens in a browser with nothing to install and no other files. Put the CSS and JavaScript inside it.

When I pick one colour, build five that go with it and show them side by side. Choose them as if they were for a slide deck.

Write the colour code under each one, and copy that code when the colour is clicked. Show a brief confirmation that it was copied.

At the top, one colour picker and one "another set" button is enough. Work out the matching colours by shifting the hue, saturation, and lightness of the one I picked, and write one line at the bottom saying which rule you used.

Text has to be readable on every swatch: use black text on light colours and white on dark ones. Do not use image files or any external address.

When you are done, go through it as if you had picked a very light colour and a very dark one. Check the text is readable in both cases, fix it if not, and give me only the final version.