A Flex container is a layout container created by setting display: flex or inline-flex. When setting display: flex, the container is a block-level element; when setting display: inline-flex, it is an inline element. Its child elements automatically become Flex projects, and can be laid out through flex-direction (define the spindle direction), justify-content (spindle alignment), align-items (cross axis alignment), flex-wrap (whether to line break), gap (project spacing) and other properties. In addition, align-self can adjust the alignment of an item individually. Flexbox is suitable for solving one-dimensional layout problems, such as horizontal or vertical centering, responsive navigation bar, uniform button distribution and spacing control, making the layout more flexible and intuitive and the code is concise.
Flexbox is a layout pattern in CSS that is used to more easily align and distribute the space of elements in containers. It is especially suitable for handling one-dimensional layouts (such as horizontal or vertical arrangements), and the Flexbox is more flexible and intuitive than traditional floating or positioning methods.

What is a Flex container?
When you set display: flex;
or display: inline-flex;
on an element, this element becomes a Flex container, and its direct child elements automatically become a Flex project.
- Using
display: flex;
will make the container become a block-level element. - Use
display: inline-flex;
to make it behave like an inline element.
Once this property is set, you can use the various properties provided by Flexbox to control how the child elements are arranged.

What are the commonly used Flexbox properties?
The core of Flexbox is that it provides a range of properties that control layout orientation, alignment, and spacing distribution. Here are some of the most commonly used:
- flex-direction : determines the direction of the spindle (i.e. the orientation of the item). Optional values are
row
(default),row-reverse
,column
,column-reverse
. - justify-content : Align items on the spindle. Common values include
flex-start
,center
,space-between
,space-around
. - align-items : Align items on cross axis. For example,
center
,flex-start
,stretch
, etc. - flex-wrap : Whether to allow project line wrapping, the default is not to wrapping. Set to
wrap
to allow the project to automatically wrap when there is insufficient space. - gap : Sets the spacing between items, and you can specify horizontal and vertical spacing at the same time, such as
gap: 10px 20px;
.
These properties are usually written on the container, while some are used to control an item separately, such as align-self
that can override align-items
set by the container.

What layout problems does Flexbox work for?
Flexbox is best at dealing with one-dimensional layouts, such as:
- Center an element horizontally or vertically
- Keep a set of buttons evenly distributed across different screen sizes
- Implement a responsive navigation bar
- Controls the spacing between multiple elements
For example, if you want a div to center vertically and horizontally in the parent container, you just need to set the parent container like this:
.container { display: flex; justify-content: center; align-items: center; }
This is much simpler than before using margin to automatically calculate or absolute positioning.
Basically that's it. After mastering these key points, you will find that using Flexbox to make page layouts will be much faster and the code will be clearer.
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