Both are used for layout of display of a website. Flexbox is one-directional layout either column or row. While grid is two-dimention- row and column both layout can used at the same time

Both are css framework. Basic difference is bootstrap has its own built frameworks, so less chance of customization. While in tailwind you can made lot of front end customization.

css box model composed of margin, border and padding. A block element total height and weight includes its margin, border and padding height and weight.

HTML5 comes with semantic tags. Which means all tags must be meaningful and synchronazied. For example, html tags composed of head and body. In the body we start with a header and then main body part and then a footer we used. This synchronization of tags are called semantic tags.