Modify CSS is a free Chrome add-on developed by Daniel that falls under the category of Browsers and the subcategory of Add-ons & Tools. This add-on aims to provide users with a convenient way to fix CSS and enhance their browsing experience.

With Modify CSS, users can easily modify the CSS of any webpage they visit. This can be particularly useful for web developers and designers who want to experiment with different styles and layouts. The add-on allows users to make changes to the CSS code in real-time and see the results instantly.

In addition to fixing CSS, Modify CSS also offers a specific feature for fixing YouTube Theater Mode. This feature enables users to enhance their viewing experience on YouTube by making adjustments to the theater mode layout. Users can customize the size, position, and other aspects of the theater mode to suit their preferences.

Overall, Modify CSS is a valuable tool for those who want to have more control over the appearance of webpages and optimize their YouTube viewing experience. It is a user-friendly add-on that can greatly enhance the customization options available to Chrome users.