Hanoi solitaire is a thing where you play with blocks and assemble towers. It's based of the Tower of Hanoi puzzle, where you move one complete tower from one space to another. In this multiple towers worth of blocks are randomly placed in several spaces (like a lot of solitaires) and you have to assemble them, moving one block at a time, which can only be placed on a larger block (or empty space), like Tower of Hanoi.
Adding free cells will be helpful for larger towers and higher tower to space ratios. You can also enable moving multiple blocks at a time which makes it much easier, even with larger towers. I still find it fun though, and it's very pleasing to assemble massive towers. It's, of course, impossible to solve with more towers than spaces, and interestingly with an equal number, it becomes almost impossible, even when allowing multiple moving or free slots. This is because you need to clear a space to place the largest block (and do that for each of the largest blocks), so effectively there does become more towers than slots. Also, having just one more space than tower seems pretty difficult, though only when moving one block at a time. I haven't tried many variations, so feel free to play around and figure out what's easy or hard (or impossible).
The HSL, LCH & okLCH colour schemes use CSS's built-in colour functions, and the rainbow gradient is a custom gradient I made which, I fell, is a more balanced rainbow.
The click to select / move input is mainly designed for mobile use as drag & drop can be inaccessible and pickup / place doesn't work without a cursor.