CSS Variable Sandbox is a Chrome add-on developed by Sean Wu Apps. As the name suggests, it serves as a playground for developers to experiment with CSS variables.

The add-on provides a draggable floating window that can be placed anywhere on the page, allowing developers to conveniently edit CSS variables and see the results in real-time. This feature enables quick and easy testing of different variable values, without the need to constantly refresh the page.

One of the notable features of CSS Variable Sandbox is the ability to copy the resulting CSS text to the clipboard with just one click. This feature comes in handy when developers want to save or share their custom CSS code.

It is important to note that due to Chrome's restrictions, variables in external stylesheets are not displayed in the sandbox. However, this limitation does not hinder the overall functionality and usefulness of CSS Variable Sandbox.

Overall, CSS Variable Sandbox is a valuable tool for developers who want to experiment with CSS variables and quickly see the impact of their changes.