What are the css selectors?

<p>CSS selectors refer to the way to specify the HTML elements to which styles are applied in CSS style sheets. Selectors are very important as they determine which HTML elements a style is bound to via CSS. CSS selectors are a basic knowledge that must be learned in CSS programming. Correct selectors can improve code readability and maintainability, and also allow developers to implement their own style rules faster. In this article, we will introduce several basic types of CSS selectors.

Element selector

<p>The element selector is one of the most basic selector types in CSS. It can select elements based on the tag name of HTML elements. For example, if we want to define the font color as red for all <p> elements, we can use the following code:

p {
  color: red;
}

<p>In this way, all paragraph text will become red.

Class selector

<p>The class selector is an identifier that selects elements based on the class attribute specified by the element. In HTML, we can specify one or more classes for an element, with each class separated by spaces. We can use class selectors to set CSS properties to specific classes.

<p class="highlight">This text will be highlighted in some way.</p>

.highlight {
  background-color: yellow;
}

<p>In this example, we set the background color of all elements with class "highlight" to yellow.

ID Selector

<p>Similar to the class selector, the ID selector selects the identifier of the element based on the ID attribute specified by the element. ID uniquely identifies an element, so each ID value is unique in each HTML document. We can use this ID selector to bind CSS properties into specific elements.

<p id="main-heading">This is the main heading of the page.</p>

#main-heading {
  font-size: 24px;
}

<p> In this example, we use the ID selector to set the font size of all elements with the ID "main-heading" to 24px.

Attribute selector

<p>The attribute selector selects the identifier of the element based on the attribute specified by the element. We can use attribute selectors to set CSS properties for all elements that have a specific attribute. The attribute selector can further determine whether the attribute matches a specific value.

<input type="text" value="Input text here">
<input type="submit" value="Submit">

input[type="text"] {
  width: 200px;
}

input[type="submit"] {
  background-color: blue;
  color: white;
}

<p> In this example, we use the attribute selector to select all <input> elements Set the width of the element with the type attribute to text to 200px, and set the background color and font color of the element with the type attribute to submit to blue. Set to white.

Pseudo-class selectors

<p>Pseudo-class selectors are selectors that select specific states or points of an element that may not be selectable through standard HTML attributes or element types. In CSS, we use colon (:) to define pseudo-class selectors.

<p>The following are several commonly used pseudo-class selectors:

<ul> <li> :hover: The state when the mouse slides over the element <li> :active: The state when the mouse clicks on the element <li> :visited: The state when the link has been visited <li> :focus: The element The state when mouse focus is obtained <li> :nth-child(): Select a sibling element of an element <li> :last-child: Select an element The last element in the sibling element

button:hover {
  background-color: red;
}

input:focus {
  outline: none;
}

ul li:nth-child(2) {
  color: blue;
}

div:last-child {
  font-size: 16px;
}

<p>In this example, we set the background color for the state when the mouse rolls over the <button> element. <input>When the element receives mouse focus, the border will be removed. We used the text color of the second <li> element of each <ul>list to be blue. For the last <div> element, we set its font size to 16px.

<p>Summary

<p>There are many types of CSS selectors, and we can use selectors according to different needs and scenarios. If we master the use of these selectors, we can greatly improve the efficiency of our CSS programming, and at the same time make our code more concise, readable and easy to maintain.

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