This little tool might be considered "not so important", but it has helped me a lot. It makes it so easy to test out…
Do you find it hard or slow to make styling adjustments to a pre-built theme?
This developer tool provides a quick way to write and add your own custom CSS, avoiding the need to directly edit a theme's files (which are overwritten when themes are updated from the marketplace).
Once installed, a toolbar button is added that opens up a popup window for writing CSS. Styles can be added and previewed immediately after saving. The popup window can be left open while navigating your site, allowing for further styling.
The styles can be stored directly within concrete5's configuration, or you can elect to store the files in it's own CSS file. You can then directly edit that file if you prefer.