12) What is CSS flexbox?

It allows you to design a flexible responsive layout structure without using any float or positioning property of CSS. To use CSS flexbox you need to define a flex container initially.

Example:

.flex-container {
display: flex;
background-color: #f4b042;
}

.flex-container > div {
background-color: #d60a33;
margin: 10px;
padding: 20px;
font-size: 30px;
}

Example of flexbox.