Bootstrap is a completely free, and open-source web development framework that helps developers to create responsive web pages. With a collection of syntax for template designs, it makes the responsive process easier, faster, and more efficient. It includes CSS and js-based theme templates for typography, navigation, buttons, forms, and other interface components.
The Tailwind CSS is a utility-first CSS framework featured with classes like text-center, flex, pt-4, and rotate-90 that enables rapidly creating custom UI (User Interface). Moreover, the Tailwind is a low-level CSS framework, which will allow you to customize it with ease. Moreover, it can be adapted to any design. The freedom and fast styling process are two main reasons behind its outstanding popularity.

CSS Box Model is basically a box which wraps around each HTML element. It consists of all the spaces margins, paddings, border and the actual content itself.
Margin: This is a space outside the elements.
Padding: This is the space inside the element or content.
Border: As the name suggests, it is a border after padding not content. Content: And the last, it is the actual content could be any HTML element.

A semantic tag in HTML is a tag whose name clearly describes its purpose and content. HTML5 introduced several new semantic tags.