Detailed analysis of the features and advantages of CSS advanced selectors

In-depth analysis of the characteristics and advantages of CSS advanced selectors

Introduction:
CSS is an essential part of web development. CSS can be used to add Style and layout. The selector is a very important part of CSS, which determines which elements in the web page apply CSS rules. In CSS, we are familiar with basic selectors, hierarchical selectors, pseudo-class selectors, etc. In addition to these common selectors, CSS also provides some advanced selectors. This article will deeply analyze the characteristics and advantages of CSS advanced selectors and provide specific code examples.

1. Attribute selector
Attribute selector is a selector that can select elements through their attributes. It can select the required elements based on their attribute values. Attribute selectors have the following forms:

1. [attribute]: Select elements with specified attributes
2. [attribute=value]: Select elements with specified attribute values
3. [attribute~=value]: Select elements with the specified attribute value, which are multiple values ​​separated by spaces
4. [attribute|=value]: Select elements with the specified attribute value or with the specified Elements starting with an attribute value, which are multiple values ​​separated by "-"
5. [attribute^=value]: Select elements starting with the specified attribute value
6. [attribute$= value]: Select elements ending with the specified attribute value
7. [attribute*=value]: Select elements containing the specified attribute value

Code example:

/* 选择所有具有title属性的元素 */
[title] {
  color: blue;
}

/* 选择具有title属性且属性值为"example"的元素 */
[title="example"] {
  background-color: yellow;
}

/* 选择具有class属性且属性值包含"box"的元素 */
[class~="box"] {
  border: 1px solid black;
}

/* 选择具有id属性且属性值以"container"开头的元素 */
[id^="container"] {
  background-color: gray;
}

/* 选择具有href属性且属性值以".com"结尾的a元素 */
a[href$=".com"] {
  color: green;
}

/* 选择具有src属性且属性值包含"logo"的img元素 */
img[src*="logo"] {
  width: 100px;
  height: 100px;
}

2. Structural pseudo-class selector
The structural pseudo-class selector is a selector that selects elements based on their positional relationship in the document. It can select the first child element, the last child element, the nth child element, etc. Structural pseudo-class selectors have the following forms:

1. :first-child: Select the first child element of the element
2. :last-child: Select the last child of the element Element
3. :nth-child(n): Select the nth child element of the element. n can be a specific number, keyword (such as "even", "odd") or formula (such as "2n", " 3n 1")
4. :first-of-type: Select the first element among all elements of the same type that have the same parent element as this element
5. :last-of-type: Select The last element among all elements of the same type that have the same parent element as this element
6. :nth-of-type(n): Select the nth element among all elements of the same type that have the same parent element as this element elements
7. :nth-last-child(n): Select the nth child element from the last of the element
8. :nth-last-of-type(n): Select the element that has The nth element from the bottom among all elements of the same type of the same parent element

Code example:

/* 选择第一个子元素，并设置颜色为红色 */
li:first-child {
  color: red;
}

/* 选择最后一个子元素，并设置背景颜色为黄色 */
li:last-child {
  background-color: yellow;
}

/* 选择偶数序号的子元素，并设置颜色为绿色 */
li:nth-child(even) {
  color: green;
}

/* 选择第三个子元素，并设置字体大小为20px */
li:nth-child(3) {
  font-size: 20px;
}

/* 选择第一个p元素，并设置边框为1px实线红色 */
p:first-of-type {
  border: 1px solid red;
}

/* 选择最后一个p元素，并设置边框为1px实线蓝色 */
p:last-of-type {
  border: 1px solid blue;
}

/* 选择li的倒数第二个子元素，并设置背景颜色为灰色 */
li:nth-last-child(2) {
  background-color: gray;
}

/* 选择同类型元素中倒数第一个元素，并设置颜色为橙色 */
span:nth-last-of-type(1) {
  color: orange;
}

3. Pseudo-element selector
The pseudo-element selector is a A selector used to select a specific part of an element rather than the entire element. It can select content in front of, behind, or at a certain position of an element, or generate some special effects. Common pseudo-element selectors have the following forms:

1. ::before: Insert the generated content before the element content
2. ::after: Insert the generated content after the element content Content
3. ::first-letter: Select the first letter of the element content
4. ::first-line: Select the first line of the element content
5. ::selection: The style applied when text is selected
6. ::placeholder: Select the placeholder text of the form control

Code example:

/* 在p元素的前面插入内容 */
p::before {
  content: "前面插入的内容";
  color: red;
}

/* 在p元素的后面插入内容 */
p::after {
  content: "后面插入的内容";
  color: blue;
}

/* 选择p元素内容的第一个字母，并设置颜色为橙色 */
p::first-letter {
  color: orange;
}

/* 选择p元素内容的第一行，并设置背景颜色为黄色 */
p::first-line {
  background-color: yellow;
}

/* 设置选中文本的样式 */
::selection {
  background-color: pink;
  color: white;
}

/* 设置输入框的占位符文本的样式 */
input::placeholder {
  color: gray;
}

Summary:
Through the structure Pseudo-class selectors, attribute selectors and pseudo-element selectors allow us to select and process elements in web pages more flexibly and achieve more fine-grained style control. These advanced selectors provide developers with more choices and powerful style expression capabilities, making the application of CSS in web development more creative and flexible. In actual development, rational use of these advanced selectors can significantly improve work efficiency and code readability.

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