myliang/x-spreadsheet ? reverse-engineered prompt

Build me a web based spreadsheet app that feels like a lightweight Excel clone in the browser.

I want a clean grid where I can click into cells, type text or numbers, select single cells or ranges, copy and paste, resize rows and columns, and use a toolbar for common formatting like bold, italic, underline, text color, fill color, borders, alignment, wrapping, merge cells, freeze rows, and undo and redo. It should support multiple sheets, basic functions, inserting and deleting rows or columns, hiding rows or columns, autofill, and data validation.

Please make it easy to load and save spreadsheet data from JavaScript, and include events for cell selection and cell edits so I can hook it up to my own app. If possible, also include simple import and export support for xlsx files, and make it work nicely in modern browsers. Look up current docs online if you need to.