Yes, it is possible to use Semantic UI or Bootstrap under Tailwind CSS. However, it is not recommended. Tailwind CSS is a utility-first CSS framework, which means that it provides individual CSS classes that can be used to style elements on a page. Semantic UI and Bootstrap are both component-based CSS frameworks, which means that they provide pre-built components that can be used to style elements on a page. If you use both Tailwind CSS and Semantic UI or Bootstrap, you will end up with a lot of CSS code in your project. This can make your code more difficult to read and maintain. It is also possible that the CSS classes from the two frameworks will conflict with each other. If you want to use Tailwind CSS, it is best to use it as your only CSS framework. This will make your code more concise and easier to maintain.