Stylebox is a free Chrome extension developed by Interesting By Default. It allows developers to inject custom cascading style sheets (CSS) into web pages. This extension is a valuable tool for designers and developers who want to quickly demonstrate different user interface and user experience designs of a web page.

With Stylebox, you can easily apply custom styles to any web page. To see how the extension works, simply follow these steps: 1) Install the Chrome extension, 2) Go to the provided URL, 3) Click on the "Stylebox" extension, and 4) Use the provided stylesheet.

The source code for Stylebox is available on GitHub, allowing developers to explore and contribute to its development. Additionally, the website of Interesting By Default showcases a compatible and suitable design for all mobile devices.

Stylebox is an excellent tool for web developers and designers looking to experiment with custom CSS and create visually appealing web pages.