I wonder if anyone can point me to where I can learn how to customize the web UI, for example, for the Query Tool, I like to have Query Editor panel stand top of the other panel on the same page. Could you please offer some input?
Just pickup the tab with your mouse and move it roughly where you want it. When the UI detects that you're over somewhere it can dock the panel, it'll highlight the drop zone.
You can dock/float most of the major panels (including dialogues) and many of the sub-panels, e.g. those within the query tool and debugger.