I enjoyed the combination of the puzzles with the tower defense genre, I have never seen anything like it! The art style is also very nice.
While viewing the game in my browser, some parts are not visible until fullscreen is selected. I have had this problem myself. In the unity engine, there is an option in project settings called resolution and presentation. There the default canvas height and width can be selected. Choosing the same dimensions as the ones being used in the editor and fullscreen mode, solved the problem in my case.
Overall a really fun game, well done!