Introduction to the Flex layout of CSS

Page layout is a key application of CSS.

Img

The traditional solution for layout, based on the box model, depends on the Display property + Position property + Float property. It is very inconvenient for those special layouts, for example, vertical centering is not easy to achieve.

Img

In 2009, a new scheme--flex layout was proposed, which could implement various page layouts in a simple, complete and responsive way. Currently, it has been supported by all browsers, which means that this feature is now safe to use.

Img

First, what is the flex layout?

Flex is the abbreviation for flexible box, meaning "resilient layout", which provides maximum flexibility for box-shaped models.
Any container can be specified as a flex layout.

. box{  Display:flex;}

Inline elements can also use the flex layout.

. box{  Display:inline-flex;}

WebKit the kernel browser, you must add the-webkit prefix. Inline elements can also use the flex layout.

. box{  Display:-webkit-flex; */Safari */  Display:flex;}

Note: After you set the flex layout, the float, clear, and vertical-align properties of the child elements are invalidated.

Ii. Basic Concepts

Elements that use flex layouts, called Flex container, are referred to as "containers." All of its child elements automatically become container members, known as Flex items (Flex Item), or "project" for short.

Img

The container has two axes by default: the horizontal spindle (main axis) and the vertical intersection axis (cross axis). The starting position of the spindle (the intersection with the border) is called main start, the end position is called the main end, the start position of the crossing axis is called Cross start, and the end position is called Cross end.
The project is arranged by default along the spindle. The main axis space occupied by a single item is called the main size, and the occupied intersection space is called cross size.

Third, the container properties

The following 6 properties are set on a container.

1. Flex-direction
2. Flex-wrap
3. Flex-flow
4. Justify-content
5. Align-items
6. Align-content

3.1 Flex-direction Properties

The Flex-direction property determines the direction of the spindle (that is, the direction in which the item is arranged).

. box {  Flex-direction:row | row-reverse | column | Column-reverse;}

It may have a value of 4. img

• Row (default): The spindle is horizontal and the starting point is on the left side.
• Row-reverse: The spindle is in the horizontal direction, starting at the right end.
• Column: The spindle is in the vertical direction, starting at the top edge.
• Column-reverse: The spindle is in the vertical direction, starting at the bottom edge.

3.2 Flex-wrap Properties

By default, items are lined up in a line (also known as the "axis"). The Flex-wrap property defines how to wrap a line if one of the axes does not fit.

Img

. box{  Flex-wrap:nowrap | wrap | wrap-reverse;}

It may take three values.
(1) nowrap (default): No Line break.

Img

(2) Wrap: Wrap, the first line is above.

Img

(3) Wrap-reverse: line break, the first line is below.

Img

3.3 Flex-flow

The Flex-flow property is a shorthand for the Flex-direction property and Flex-wrap property, and the default value is row nowrap.

. box {  flex-flow: <flex-direction> | | <flex-wrap>;}

3.4 Justify-content Properties

The Justify-content property defines how the item is aligned on the spindle.

. box {  Justify-content:flex-start | flex-end | center | space-between | Space-around;}

Img

It may take 5 values, and the exact alignment is related to the direction of the axis. The following assumes that the spindle is from left to right.

• Flex-start (default): Left Justified
• Flex-end: Right-justified
• Center: Center
• Space-between: Justified, the interval between items is equal
• Space-around: The intervals on each side of the item are equal. Therefore, the interval between items is one times larger than the interval between items and borders.

3.5 Align-items Properties

The Align-items property defines how the item is aligned on the intersection axis.

. box {  Align-items:flex-start | flex-end | center | baseline | stretch;}

It may take 5 values. The specific alignment is related to the direction of the cross axis, which assumes that the intersection axis is from top to bottom. img

• Flex-start: Start alignment of the intersection axis
• Flex-end: End alignment of the intersection axis
• Center: Midpoint alignment of the intersection axis
• Baseline: Baseline alignment for the first line of text in a project
• Stretch (default): If the item is not set to height or auto, it fills the height of the entire container

3.6 Align-content Properties

The Align-content attribute defines the alignment of multiple axes. If the item has only one axis, this property does not work.

. box {  Align-content:flex-start | flex-end | center | space-between | space-around | stretch;}

Flex-start: Aligned with the start of the intersection this property may take 6 values.

• Flex-end: Aligns with the end of the intersection axis
• Center: Aligns with the midpoint of the intersection axis
• Space-between: aligned with the intersection axis, evenly spaced between axes
• Space-around: The intervals between each axis are equal. So, the intervals between the axes are one times greater than the intervals between the axes and the borders.
• Stretch (default): Axis fills the entire cross axis

Iv. Properties of the project

The following 6 properties are set on a project.

• Order
• Flex-grow
• Flex-shrink
• Flex-basis
• Flex
• Align-self

4.1 Order Property

The Order property defines the order in which the items are arranged. The smaller the number, the higher the alignment, and the default is 0.

. Item {  order: <integer>;}

4.2 Flex-grow Properties img

The Flex-grow property defines the magnification of the item, which defaults to 0, that is, if there is space left, it is not zoomed in.

. Item {  Flex-grow: <number>;/* Default 0 */}

Img

If all items have a Flex-grow property of 1, they will divide the remaining space (if any). If the Flex-grow property of one project is 2 and the other items are 1, the former occupies more than the remaining space.

Img

4.3 Flex-shrink properties

The Flex-shrink property defines the scaling of the project, which defaults to 1, which means that if there is not enough space, the project shrinks.

. Item {  Flex-shrink: <number>;/* Default 1 */}

Img

If all items have a Flex-shrink property of 1, they will be scaled down when there is not enough space. If the Flex-shrink property of an item is 0 and the other items are 1, the former does not shrink when there is not enough space.
A negative value is not valid for this property.

Img

A negative value is not valid for this property.

4.4 Flex-basis Properties

The Flex-basis property defines the spindle space (main size) that the item occupies before allocating the extra space. Based on this property, the browser calculates whether the spindle has extra space. Its default value is auto, which is the original size of the project.

. Item {  flex-basis: <length> | auto;/* Default auto */}

It can be set to the same value as the width or height property (such as 350px), then the item will occupy a fixed space.

4.5 Flex Properties

Flex properties are shorthand for Flex-grow, Flex-shrink, and flex-basis, and the default value is 0 1 auto. The latter two properties are optional.

. item {  Flex:none | [< ' Flex-grow ' > < ' Flex-shrink ';? | | < ' flex-basis ' >]}

　　

This property has two shortcut values: Auto (1 1 Auto) and none (0 0 Auto).
It is recommended that you use this property instead of writing three separate properties separately, because the browser calculates the relevant values.

4.6 Align-self Properties

The Align-self property allows a single item to be aligned differently from other items, overriding the Align-items property. The default value is auto, which represents the Align-items property that inherits the parent element, and, if there is no parent element, is equivalent to stretch.

. item {  Align-self:auto | flex-start | flex-end | center | baseline | stretch;}

Img

This property may take 6 values, except auto, and the other is exactly the same as the Align-items property.

If you think the article is good, please Bo Master drink a cup of tea Oh!!!

Introduction to the Flex layout of CSS