This is my take on a design option. I prefer more of a dark theme as well as a background that goes well with it. I also improved the icon animations as the mouse hovers over it and when the apps are opened. I fixed the bug where the dock disappears after opening one app. See the code for how I fixed it. Lastly I added a menu for the widgets.
Suggestions: If you really want to make the best OS on scratch and want to collaborate efficiently I would recommend you leave notes in the program explaining what your code does so that no one else wastes their time making code that already exists or trying to figure out what a piece of code does. I really like the ability to go in and out of fullscreen on the apps although I believe it would be hard if we were to "hard code" the location of each item in the UI of an app (ex. When its fullscreen mode go here, when its minimized go here) I would suggest we instead program the items location based on the size of the window so that windows can be resized to a custom size which would be really cool. (update: after inspecting the code it does appear that you have a system going that is somewhat similar the user just can't resize the window to a custom size yet.)
