Plunker

C++Builder is a fast, integrated design and development suite for modern apps. Are you ready to design the best UIs of your life? Our award winning VCL framework for Windows and FireMonkey (FMX) visual framework for cross-platform UIs provide you with the foundation for intuitive, beautiful user interfaces that wow on every platform: Windows, macOS, iOS, and Android. Design your master UI layout once, then easily customize platform- and device-specific views without duplication of design effort. Drag-and-drop visual and non-visual components from the palette using our visual designer. Visually connect user interface elements to data sources using the LiveBindings Designer. Real-time design validation using Live On-Device Preview to broadcast the active form to multiple devices simultaneously. Add responsive design with resolution-aware components for desktop, tablets, and smartphones. Real, platform-specific native controls for an improved user experience.

JSFiddle has the notion of panels (or tabs if you switch into the tabbed layout), there are 4 panels, 3 where you can enter code, and 1 to see the result: HTML - structure code, no need to add body doctype head, that's added automatically, CSS - styles. You can switch pre-pocessor to SCSS, JavaScript - behavior. There are many frameworks and code pre-processors you can use. Once you enter code, just hit "Run" in the top actions bar, and the fourth panel with results will appear. SFiddle 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).