display: flex;

The CSS property "display: flex;" is used to create a flexible (or "flex") container that can dynamically adjust the size and position of its child elements. This property is often used for layout purposes, allowing web developers to create complex and responsive page designs more easily.

When "display: flex;" is applied to a parent element, it turns the element into a "flex container". This means that the child elements of the container can be positioned and sized using various flexbox properties, such as "flex-direction", "justify-content", and "align-items".

Here's an example of how "display: flex;" can be used to create a simple row of three equal-sized boxes:

HTML:

<div class="flex-container">
<div class="box"></div>
<div class="box"></div>
<div class="box"></div>
</div>

CSS:

.flex-container {
display: flex;
}

.box {
width: 100px;
height: 100px;
background-color: red;
margin-right: 10px;
}

In the above example, the parent element (with the "flex-container" class) has "display: flex;" applied to it, which turns it into a flex container. The child elements (with the "box" class) are then positioned next to each other horizontally, with a 10px margin between them, thanks to the default value of "flex-direction" being "row".

Overall, "display: flex;" is a powerful CSS property that allows web developers to create flexible and responsive layouts with ease.