To be honest, apart from the presentation (typical Unity-style ugly buttons), I have no complaints. A really solid puzzle game that could become commercial with a little more polishing.
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Sorry, after checking again these are not as bad as I remembered, I thought they were smooth-textured, like the default button textures in Unity that beginner game developers use even when the art style of the rest of the game is greatly contrasting (e.g. pixel art). But I think there are still some improvements to be made - bigger contrast between the text and button texture, more matching colors (https://coolors.co/generate) and not making a weird grey box when you hold down the mouse button. Little things like that.