Detailed explanation of CSS Flex flexible layout and its application techniques

Detailed explanation of CSS Flex elastic layout and its application techniques

Introduction:
Flexible layout (Flex) is a new layout model introduced in CSS3. Able to automatically adjust the size and position of child elements in a container to adapt to different container sizes. Use Flex layout to quickly implement complex web page layouts with good responsiveness.

1. Basic concepts of Flex layout
Flex layout consists of a container and child elements. The container is an element with the display:flex or display:inline-flex attribute, and the child elements are called Flex items.

1.1 Container properties
Containers control the layout of Flex items through some properties. Commonly used properties include:

• flex-direction: Set the direction of the main axis, which can be row ( horizontal direction), column (vertical direction), row-reverse (reverse horizontal direction), column-reverse (reverse vertical direction).
• flex-wrap: How to wrap, it can be nowrap (no line wrap), wrap (line wrap), wrap-reverse (line wrap and reverse).
• justify-content: Alignment on the main axis, which can be flex-start (start alignment), flex-end (end alignment), center (center alignment), space-between (alignment at both ends, project space-around (equal spacing between items), space-around (equal spacing on both sides of each item).
• align-items: Alignment on the cross axis, which can be flex-start (start alignment), flex-end (end alignment), center (center alignment), baseline (baseline alignment), stretch ( stretched to fill the container).
• align-content: In the case of multiple lines, the alignment of each line on the cross axis can be flex-start (start alignment), flex-end (end alignment), center (center alignment), space -between (aligned ends, equal spacing between rows), space-around (equal spacing on both sides of each row), stretch (stretched to fill the container).

1.2 Properties of Flex items
Flex items control their own layout through some properties. Commonly used properties include:

• flex-grow: Specify the magnification ratio of the item , the default is 0, that is, no amplification.
• flex-shrink: Specify the shrinkage ratio of the item, the default is 1, that is, if there is insufficient space, the item will shrink.
• flex-basis: Defines the main axis space occupied by items before allocating excess space.
• flex: is the abbreviation of flex-grow, flex-shrink and flex-basis. The default value is 0 1 auto.
• align-self: Allows a single item to be aligned differently from other items on the cross axis.

2. Application skills of Flex layout
Flex layout has many skills in practical application that can help us handle the layout better. Here are some common application skills.

2.1 Equal-height layout
Using Flex layout, you can easily implement equal-height layout. You only need to set align-items: stretch on the container to make all Flex items occupy the same height on the cross axis.

Sample code:

.container {
  display: flex;
  align-items: stretch;
}

2.2 Horizontal centering
To achieve horizontal center alignment, just set justify-content: center on the container.

Sample code:

.container {
  display: flex;
  justify-content: center;
}

2.3 Vertical centering
To achieve vertical center alignment, just set align-items: center on the container.

Sample code:

.container {
  display: flex;
  align-items: center;
}

2.4 Adaptive left and right columns
The width of the left column is fixed, and the right column is adaptive according to the remaining width of the container.

Sample code:

.container {
  display: flex;
}

.left {
  flex: 0 0 200px; /* 左栏宽度为200px */
}

.right {
  flex: 1; /* 右栏自适应宽度 */
}

2.5 Order adjustment
Flex layout allows you to adjust the order of Flex items through the order attribute.

Sample code:

.container {
  display: flex;
}

.first {
  order: 2; /* 放到第二位 */
}

.second {
  order: 1; /* 放到第一位 */
}

Conclusion:
By flexibly using the properties and techniques of Flex layout, we can easily implement various complex web page layouts with good responsiveness. Mastering Flex layout will greatly improve our CSS layout capabilities.

Summary:
This article introduces the basic concepts and common properties of CSS Flex elastic layout in detail, and also shares some common application techniques. We hope that the introduction in this article can help readers better understand and use Flex layout, and improve the effectiveness of web page layout and development efficiency.

Reference:

• CSS Tricks - A Complete Guide to Flexbox: https://css-tricks.com/snippets/css/a-guide-to-flexbox/
• MDN Web Docs - Flexbox: https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Flexible_Box_Layout/Basic_Concepts_of_Flexbox

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