To kill a panel, use
Ctrl + key
Learn by example: cssreference.io is a free visual guide to CSS. It features the most popular properties, and explains them with illustrated and animated examples.
This document is a collection of Unix/Linux/BSD commands and tasks which are useful for IT work or for advanced users. This is a practical guide with concise explanations, however the reader is supposed to know what s/he is doing.
A very useful list off all the Emacs functions and variables accessible from the web or you mobile. It is also possible to access to this from Emacs itself by invoking