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An article introducing the definition method of CSS

PHPzOriginal: 2023-04-21 11:22:321117browse

CSS (Cascading Style Sheets) is a language used for web page style design. It controls the appearance and layout of web pages by defining styles. This article will introduce how to define CSS.

Definition of CSS

Internal definition

In HTML files, you can use <style> in the tag tags to define CSS styles, such definitions are called internal styles.

<head>
  <style>
    p {
      color: red;
    }
  </style>
</head>

In this example, we define the text color of the  element to be red. All CSS styles should be written in <style> tags.

External definition

In HTML files, you can also use external style sheets. An external style sheet is a separate file containing CSS styles, with the suffix .css. This can be introduced into an HTML file using the <link> tag.

<head>
  <link rel="stylesheet" type="text/css" href="style.css">
</head>

This code introduces the external style sheet style.css into the HTML document. The href attribute specifies the location of the style sheet.

Inline definition

In addition to defining styles internally and externally, styles can also be defined inline within HTML elements. This way of definition is called inline style.

<p style="color: red;">Hello World!</p>

In this example, we define a color style for the  element using the style attribute.

CSS syntax

CSS syntax consists of selectors, attributes and values. We can use selectors to select a page element and then set its properties and values.

Selector

A selector is an identifier used to select elements. The following are some common selector types:

Tag selector: Select all elements of this tag type in the page, such as p, div, a.
Class selector: Select elements with the same class in the page, such as .carousel.
ID selector: Select elements with the same ID in the page, such as #header.
Attribute selector: Select elements based on their attribute values, such as [type="text"] Select all elements whose type value is text.
Pseudo-class selector: Set styles for elements in specific states, such as :hover, :active.

Properties and Values

Properties are specific characteristics of a style, such as color, font size, padding, etc. The value is the specific style applied to the attribute, such as red, 12pt, 20px, etc.

The following are some common properties and values:

color: Set the text color, such as color: red;.
font-family: Set the font family, such as font-family: Arial, sans-serif;.
font-size: Set the font size, such as font-size: 16px;.
background-color: Set the background color, such as background-color: #f0f0f0;.
border: Set the border, such as border: 1px solid black;.
margin: Set the outer margin of the element, such as margin: 10px;.
padding: Set the inner margin of the element, such as padding: 10px;.
width: Set the element width, such as width: 100px;.
height: Set the element height, such as height: 100px;.

CSS Example

The following example demonstrates how to set the color and width properties of the ID selector:

<head>
  <style>
    #header {
      background-color: #333333;
      color: #ffffff;
      width: 100%;
      text-align: center;
    }
  </style>
</head>

<body>
  <div id="header">
    <h1>Hello World!</h1>
  </div>
</body>

In this example, we have an ID of The header element sets the background color, text color, width, and text alignment. We used the tag selector to select the heading element <h1>.

Summary

This article introduces the definition method, syntax, selectors and properties of CSS. Armed with this knowledge, you can easily use CSS to design and control the style and layout of your web pages. When you need more learning and practice materials about CSS, check out CSS tutorials and resources online.

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