First, SUW is great! But everything can get better… like the panels on the right. Currently you can close a panel only by cliking the X at the right hand of the panel title. Before finding those, I was intuitively trying to close each by clicking on the opened panel logo. But it just rolled into view and didn’t close. It is OK that a panel comes into view, the next click could, however, close it. I think, it would be much easier for panel navigation. Especially because the borders between them are not clearly visible and the X for closing a panel only shows when you hoover over the title.
No. This idea is contrary to established UI design for collapsible / expanding docked panels.
It has been already established that clicking the header bar of a panel window toggles between expanded and collapsed states.
This is how the desktop editions of SketchUp also work and comes from the OS (at least MS Windows) UI frameworks used for the application. The (free) web edition attempts to keep as many interface features as possible similar to the desktop editions. (This cuts down the learning curve when moving to the desktop editions, and visa versa.)
This cannot be done, but perhaps a click on the panel’s blue icon tab in the right sidebar could toggle an open panel closed again. (Currently clicking a tab icon does nothing if it’s panel is already open and expanded. It will expand collapsed panels and open closed panels however.)
By design, and standard UI behavior.
This is styling design that has recently become more popular since Windows 8’s flat UI came out.
(Microsoft thinks that they are saving processing power for other things when they do not need to render UI elements that are not actually in use. They also do this for scroll bars.)
I personally dislike hidden UI elements. I do not like having to “explore” the UI with my mouse to find hidden controls.
Anyway, the hidden close button could be made always visible.