Flexbox, or "Flexible Box Layout," is a design module in CSS3 that provides a more efficient way to distribute space between the elements of a container, even when their size is dynamic or unknown. This is especially useful for designing responsive and complex layouts without the need to use floats or complicated positioning.

Why Use Flexbox?

The main goal of Flexbox is to give the container the ability to alter the width, height, and order of the elements, to best fill the available space (mainly to accommodate all devices and screen types). Flexbox is also a more suitable and powerful solution for designing web applications and complex layouts.

Main Advantages of Flexbox

1. Equal Space Distribution: Flexbox allows you to evenly distribute elements within the container.
2. Easy Alignment: You can easily align elements both vertically and horizontally.
3. Element Reordering: It allows you to reorder elements without altering the HTML.
4. Easy Responsiveness: Making your website responsive is much simpler and straightforward with Flexbox.

Basic Example

Let's look at a simple example of how Flexbox can be implemented:

html

In this example, the .flex-container container has its children .flex-item arranged in a horizontal row, thanks to the display: flex; property.

Placement of Flexbox in the CSS Structure

Flexbox is very simple to use. You just need to add the display: flex; property to a container, and automatically all its child elements become Flex items (flex-items). You can then use several additional properties to adjust the behavior and arrangement of these items.

Illustrative Images

1. [Placeholder: Image showing how flex elements are distributed in a row within a container with display: flex;. Similar example to the code above with three elements in a row.]

In summary, Flexbox is a powerful and flexible tool for efficiently and effectively creating modern, responsive web designs.