Bootstrap gives you a pre-made look and feel that you can use despite knowing CSS or not and maybe you can customize a bit, make a theme, etc. Bootstrap is more like "Tailwind UI" which is different thing from Tailwind (the tool).

To use plain Tailwind (without Tailwind UI) you do need to know CSS. It's just like a "CSS-in-JS" tool, except it's "CSS-in-HTML" this time.