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What are the ways to introduce css?

青灯夜游Original: 2021-04-28 15:20:0319819browse

The ways to introduce css are: 1. Use the style attribute of the HTML tag to introduce it; 2. Write the style code in the "c9ccee2e6ea535a969eb3f532ad9fe89531ac245ce3e4fe3d50054a55f265927" tag pair on the page; 3. Use link tag to introduce external CSS files; 4. Use the "@import" rule to introduce external CSS files.

The operating environment of this tutorial: Windows 7 system, CSS3&&HTML5 version, Dell G3 computer.

1. Use the style attribute of the HTML tag (inline)

Add the style attribute directly to a single HTML element tag to control the presentation style of the HTML tag.

This way of introducing CSS is decentralized, flexible and convenient, but it lacks integrity and planning, which is not conducive to later modification and maintenance. When the style of the website needs to be modified, the same modification may involve multiple places. , high maintenance costs. The style effect using the STYLE attribute is the strongest and will overwrite the same style effects of other introduction methods.

<div style="color:red"></div>

2. Use the style tag (embedded)

Write the style code on the pagec9ccee2e6ea535a969eb3f532ad9fe89...531ac245ce3e4fe3d50054a55f265927 Among tags

c9ccee2e6ea535a969eb3f532ad9fe89...531ac245ce3e4fe3d50054a55f265927 tag structure can be located anywhere in the page6a74014ee44f5deb5894267f99b68016 tag, or can appear multiple times. Usually the entire c9ccee2e6ea535a969eb3f532ad9fe89...531ac245ce3e4fe3d50054a55f265927 structure is written in the 93f0f5c25f18dab9d176bd4f6de5d30e...9c3bca370b5104690d9ef395f2c5f8d1 section of the page. The characteristic of this way of introducing CSS is that the CSS code of each page may be unified and planned. It is easy to reuse and maintain within a page, but the reuse of CSS code between multiple pages is still not enough.

<style>
 bdoy{font-size:14px;}
</style>

3. Use the link tag to introduce external CSS files (linked)

Write the css code in a separate file and use the link tag to directly introduce the file to the page. A page can use the LINK tag multiple times to introduce multiple external CSS files. Pay attention to the mutual influence of these CSS codes. Usually, the CSS files introduced later will overwrite the same effects of the CSS files introduced earlier. This method of introducing CSS is currently the most popular. CSS codes can be planned within the scope of each website to facilitate reuse and maintenance. However, this highly centralizes the code, and the amount of code may be too large, and it is easy to cause problems if it is not properly maintained. confusion.

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

4. Use @import to introduce CSS files (import type)

There are two ways to use @import to introduce CSS files, one can be placed on the page c9ccee2e6ea535a969eb3f532ad9fe89...531ac245ce3e4fe3d50054a55f265927, the usage is as follows:

@import url(index2.css);

It can also be used in a CSS file, the usage is as follows:

@import "sub.css";

You can use @import to introduce CSS It is very convenient to introduce CSS code from external files for maintenance and planning. However, every time an additional CSS file is introduced, a connection request will be added to the server. When the number of visits is large, a trade-off needs to be made between maintainability and performance. (Learning video sharing: css video tutorial)

The difference between link type and import type

##2cdf5bf648cf2f33323966d7f58a7f3f

1, Belongs to XHTML

2, Prioritizes loading CSS files to the page

@import

1, Belongs to CSS2.1

2. Load the HTML structure first and then load the CSS file.

Priority in CSS

1. Style priority

Inline style>Internal style>External style (the last two The latter is the principle of proximity)

For example:

Comparison priority between inline style and internal style:

<!DOCTYPE>
<html>
<head>
  <meta charset="utf-8" />
  <title>行内样式和内部样式表的优先级</title>
    <!--内部部样式表-->
  <style type="text/css">
    p{
      color: blue;
    }
  </style>
</head>
<body>
     <!--行内样式-->
     <p style="color: red;">我是p段落</p>
</html>

Browser running effect:

Conclusion: Inline styles have higher priority than internal style sheets.

Comparison priority between internal style sheet and external style sheet:

a. Internal style sheet is above external style sheet

<!DOCTYPE>
<html>
<head>
  <meta charset="utf-8" />
  <title>内部样式表和外部样式表的优先级</title>
    <!--内部部样式表-->
  <style type="text/css">
    p{
      color: blue;
    }
  </style>
  <!--外部样式表-->
  <link rel="stylesheet" type="text/css" href="css/style.css" /> 
</head>
<body>
     <p>我是p段落</p>
     <p>我是p</p>
     <ol>
         <li>1111</li>
         <li>2222</li>
     </ol>
</html>

Browser running effect:

b. The external style sheet is above the internal style sheet

<!DOCTYPE>
<html>
<head>
  <meta charset="utf-8" />
  <title>内部样式表和外部样式表的优先级</title>
    <!--外部样式表-->
  <link rel="stylesheet" type="text/css" href="css/style.css" /> 
    <!--内部部样式表-->
  <style type="text/css">
    p{
      color: blue;
    }
  </style>
</head>
<body>
     <p>我是p段落</p>
     <p>我是p</p>
     <ol>
         <li>1111</li>
         <li>2222</li>
     </ol>
</html>

Browser running effect:

Conclusion: Internal Style sheets and external style sheets use the principle of proximity, that is, whoever writes below shall prevail.

Note: Import and link priorities also use the proximity principle.

2. Selector priority

Priority: ID selector>Class selector>Tag selector

<!DOCTYPE>
<html>
<head>
  <meta charset="utf-8" />
  <title>选择器的优先级</title>
  <style type="text/css">
    #a{
      color: green;
    }
    .b{
      color: yellow;
    }
    h2{
      color: red;
    }
  </style>
</head>
<body>
     <h2>111</h2> <!--红色-->
     <h2 id="a" class="b">222</h2> <!--绿色-->
     <h2 class="b">333</h2><!--黄色-->
</html>

Browser running effect:

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