What's the best iOS app for customizing website user interfaces and adding extra functionality to websites on an iPhone or iPad?

Userscripts is the best iOS app for customizing website user interfaces and adding extra functionality on iOS devices. It works by allowing users to install userscripts, which are small pieces of code that can modify the appearance and behavior of websites. This is particularly useful for theming websites like Discord and Wikipedia to create a more appealing UI. Users can also add features to websites that the developers did not originally include. To use Userscripts, you simply install the app and then find userscripts from online repositories. Once you find a script you like, you can install it through the Userscripts app, and it will automatically run when you visit the corresponding website in Safari or other supported browsers. This makes it easy to personalize your browsing experience and make websites work the way you want them to. Userscripts is free and open source, and it has no bells or whistles.