CUBEFISH is a Chrome extension developed by Naitzirch that allows users to customize the background of websites. With this extension, users can choose from a variety of presets, opt for full color backgrounds, or even add their own image as the background using an image URL.

One of the standout features of CUBEFISH is its ability to apply backgrounds to single pages, entire websites, or specific pages that match a certain URL pattern on a particular domain. However, it's important to note that this extension currently only changes the background of the HTML `body` element of a website. As a result, it may not work on websites where the `body` element is not visible.

CUBEFISH is a free extension that falls under the Browsers category and specifically the Add-ons & Tools subcategory. It provides users with a simple and straightforward way to personalize their browsing experience by adding a custom background to their favorite websites.