Here are few short cut keys that you can use in Space in webGL or in Desktop build.
To start flying you can press "F" key.
Once your character is hovering press "E" Key to go higher, or "C" to go Lower.
You can hold Shift key while flying to fly faster; same key can be used while walking to run.
This is a hidden key which shows a profiler showing the performance of a region.
To toggle this window Hold "Shift" Key and press ` Key.
To toggle Space between fullscreen and windowed mode press F11 Key(Windows), Command(⌘) + F(Mac OS).
Press the F9 key or Alt+U to toggle the user interface on/off.