How to use css selector

CSS (Cascading Style Sheet) selector is a tool used to select HTML elements. CSS selectors allow you to style HTML elements based on their type, attribute, ID, or class. Selectors are the foundation of CSS, and mastering them is an important step in mastering CSS.

This article will introduce commonly used CSS selectors and their usage. Before you start, you need to understand some basic knowledge:

1. CSS selector syntax: The selector points to the HTML element, followed by a pair of curly braces {}, and within the curly braces is a set of attribute and value pairs , separated by semicolons.
2. HTML elements can use tag names, class names (id) and attributes as selectors.
3. Elements can have multiple class names, separated by spaces.
4. ID and class names must follow naming rules, such as not starting with a number, not containing special characters, etc.

Now let us learn more about several CSS selectors and how to use them.

1. Tag Selector

The tag selector is the simplest CSS selector. It uses the tag name of the HTML element to set the style. The tag selector applies to all elements of this tag.

For example, to set the red text color for all paragraphs (p), you can use the following code:

p {
  color: red;
}

2. Class Selector

Class Selector The selector selects elements by adding the class name in the tag. Class names start with the "." symbol.

For example, the following code will set the text color to red for all elements using the "my-class" class name:

.my-class {
  color: red;
}

In HTML, the class attribute can be applied to any element. Here is an example:

<div class="my-class">我是一个含有my-class类名的div元素</div>

3. ID Selector

The ID selector selects elements by adding the ID name in the tag. The ID name starts with the "#" symbol.

For example, the following code will set the text color of the element with the ID "my-id" to blue:

#my-id {
  color: blue;
}

In HTML, the id attribute can only be applied to a single element. Here is an example:

<div id="my-id">我是一个含有my-id ID名称的div元素</div>

4. Attribute Selector

Attribute selector sets styles based on the attributes of the HTML element. They allow access to an element's properties using square brackets [].

For example, the following code will set the text color to green for all elements with the "href" attribute:

a[href] {
  color: green;
}

Alternatively, you can use the attribute value to set the style more granularly. For example, the following code will set the text color of all links whose "href" attribute value ends with ".pdf" to red:

a[href$=".pdf"] {
  color: red;
}

In the above code, the "$=" symbol means that the attribute value ends with a certain ending with a specific value.

5. Descendant Selector

Descendant selector sets styles by selecting child elements of a parent element. It uses spaces to separate each tag name.

For example, the following code will set the a element in all div elements to green:

div a {
  color: green;
}

In the above code, the space character connects the div element and the a element to each other.

6. Intersection Selector

The Intersection Selector selects elements with both the specified class name and tag name. It is defined using "." and the tag name.

For example, the following code will set the text color to blue for all elements with a "my-class" class name and a "li" tag name:

li.my-class {
  color: blue;
}

In the above code, "li The .my-class" selector only applies to elements with both "li" and "my-class" class names.

Summary:

So far, we have learned about 6 commonly used CSS selectors. Understanding selectors will help you better position and develop styles for HTML elements. Different selectors require different HTML structures, so we need to choose the appropriate selector according to actual needs.

CSS selectors are a very important knowledge point in CSS. For front-end developers, mastering them is a very important step. Hope this article can help you.

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