Comment on page
JSFiddle allows you to switch the layout of the editor from the classic 2x2 grid to something that suits your needs. In addition to the grids mode it also has a tabbed mode.
Grids are fully resizable. As an addition resizing the Results panel will tell you its width (handy for working on media queries).
There are two themes to choose from: Dark (default) and Light. Light theme has been retired.