Introduction to css

Today’s study finally came to CSS. CSS can realize many cool interfaces, and CSS appeared to solve the problem

A language that came into being due to the chaos of writing styles on the HTML structure. In the past, styles were written together with the structure.

No distinction is made between each other, and this greatly increases the amount of code, because the same style is repeated repeatedly and can only be rewritten again

Later, it also made it difficult to read the code after it was written, and it became extremely difficult to find errors. At this time, css appeared and

Reflects its benefits, and its benefit is to solve the above problems and separate structure from performance.

Now let’s talk about what is css?

What is CSS?

CSS (Cascading Style Sheets) cascading style sheets

CSS3 is an upgraded version of CSS2. 3 is just the version number. It adds many powerful new features based on CSS2.1.

Currently, the mainstream browsers chrome, safari, firefox, opera, and even 360 already support most of the CSS3 functions

, IE10 will also begin to fully support CSS3. Different browsers may require different prefixes. It represents that CSS property

or rules have not yet become part of the W3C standard and are private properties of the browser, although newer versions of browsers currently do not require them

A prefix is ​​required, but for better forward compatibility, the prefix is ​​still indispensable.

CSS appeared to decorate the structure of HTML. It can do things that previous HTML could not do. It can decorate HTML

It’s very beautiful, so css is a complement to HTML.

For example:

<span style="color: #0000ff;"><!</span><span style="color: #ff00ff;">DOCTYPE html</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">html </span><span style="color: #ff0000;">lang</span><span style="color: #0000ff;">="en"</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">meta </span><span style="color: #ff0000;">charset</span><span style="color: #0000ff;">="UTF-8"</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>css<span style="color: #0000ff;"></</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span><span style="background-color: #f5f5f5; color: #800000;">
    p</span><span style="background-color: #f5f5f5; color: #000000;">{</span><span style="background-color: #f5f5f5; color: #ff0000;">
        color</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> #ff00ff</span><span style="background-color: #f5f5f5; color: #000000;">;</span><span style="background-color: #f5f5f5; color: #ff0000;">
        font-size</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 16px</span><span style="background-color: #f5f5f5; color: #000000;">;</span><span style="background-color: #f5f5f5; color: #ff0000;">
        font-weight</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> bold</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
    <span style="background-color: #f5f5f5; color: #000000;">}</span>
    <span style="color: #0000ff;"></</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>wowaoda<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">html</span><span style="color: #0000ff;">></span>

css modifies the p tag so that the font is pink, bold, and the font size is 16 pixels. From this, we can see that css can add styles to elements in HTML, that is, modify it and dress it up.

So what exactly can css do?

What can CSS do? ? ? ?

CSS can achieve many effects and even animation effects that previously required the use of images and scripts in just a few lines of code.

Such as rounded corners, picture borders, text shadows and box shadows, transitions, animations, etc.

CSS simplifies the design process for front-end developers, providing more flexible page layout and faster page loading speed.

All web page styles on the site can be controlled using a CSS file. Just modify the corresponding code in the CSS file,

Then all pages of the entire site will change accordingly. CSS can support a variety of devices, such as mobile phones, PDAs, printers, televisions, game consoles, etc.

Purpose: Separate performance from structure.

Example:

Code

<span style="color: #0000ff;"><!</span><span style="color: #ff00ff;">DOCTYPE html</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">html </span><span style="color: #ff0000;">lang</span><span style="color: #0000ff;">="en"</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">meta </span><span style="color: #ff0000;">charset</span><span style="color: #0000ff;">="UTF-8"</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>css<span style="color: #0000ff;"></</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span><span style="background-color: #f5f5f5; color: #800000;">
    div</span><span style="background-color: #f5f5f5; color: #000000;">{</span><span style="background-color: #f5f5f5; color: #ff0000;">
        width</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 100px</span><span style="background-color: #f5f5f5; color: #000000;">;</span><span style="background-color: #f5f5f5; color: #ff0000;">
        height</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 100px</span><span style="background-color: #f5f5f5; color: #000000;">;</span><span style="background-color: #f5f5f5; color: #ff0000;">
        border-radius</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 50%</span><span style="background-color: #f5f5f5; color: #000000;">;</span><span style="background-color: #f5f5f5; color: #ff0000;">
        background</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> rgba(200,150,200,0.3)</span><span style="background-color: #f5f5f5; color: #000000;">;</span><span style="background-color: #f5f5f5; color: #ff0000;">
        box-shadow</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 2px 2px 2px 3px #eee</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
    <span style="background-color: #f5f5f5; color: #000000;">}</span>
    <span style="color: #0000ff;"></</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">div</span><span style="color: #0000ff;">></</span><span style="color: #800000;">div</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">html</span><span style="color: #0000ff;">></span>

This is completely realized by css, which beautifies the page.

Also please click this: css for animation

So what I wrote above makes me curious about its power. Next, let’s explore its language.

CSS syntax structure?

CSS syntax consists of three parts: selectors, attributes and values

attribute is the style attribute you wish to set.

Each attribute has a value. Properties and values ​​are separated by colons.

<span style="color: #000000;">p{
    font-size:15px;
    }</span>

p is the selector, the attribute is font-size, and the value is 15px;

<span style="color: #000000;">a{
    color:#000;
    }</span>

This is also understood in the same way, is it very similar? Its structure is very simple, just these three parts.

Now that you understand all the css, how do you implement these css? Then let’s talk about quoting to the page.

How to introduce CSS?

Three introduction methods:

1. Inline quotation Inline quotation refers to writing CSS style encoding directly in the style attribute in the HTML tag.

Note that when introducing CSS in this way, there is no need to write a selector.

<span style="color: #0000ff;"><</span><span style="color: #800000;">p </span><span style="color: #ff0000;">style</span><span style="color: #0000ff;">="color:#ff7600;"</span><span style="color: #0000ff;">></span>我是段落<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>

2. On-page citation

In-page references are a separate part of the page, positioned within by the tag.

<span style="color: #0000ff;"><</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">meta </span><span style="color: #ff0000;">charset</span><span style="color: #0000ff;">="UTF-8"</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>css<span style="color: #0000ff;"></</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span><span style="background-color: #f5f5f5; color: #800000;">
    p</span><span style="background-color: #f5f5f5; color: #000000;">{</span><span style="background-color: #f5f5f5; color: #ff0000;">
        color</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> #ff7600</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
    <span style="background-color: #f5f5f5; color: #000000;">}</span>
    <span style="color: #0000ff;"></</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>

3.External style sheet

External style sheet is the best form of CSS application. It places the CSS style code separately in an external file and then calls it by the web page.

<span style="color: #0000ff;"><</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">meta </span><span style="color: #ff0000;">charset</span><span style="color: #0000ff;">="UTF-8"</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>css<span style="color: #0000ff;"></</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">link </span><span style="color: #ff0000;">rel</span><span style="color: #0000ff;">="stylesheet"</span><span style="color: #ff0000;"> href</span><span style="color: #0000ff;">="style.css"</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>

这些就是它的引用方式，只要引用进来才能作用到HTML结构上。

既然有这几种引用方式，那么是不是随意引用的呢？如果这样那么就是乱套了，因为css也叫层叠样式表，既然

随便引用那么不是和它的理念冲突了吗？所以这些引用还是规则的，就是优先级；

优先级依次是：就近原则

行内引用 > 页内引用 > 页外引用

DOCTYPE html>
<html lang="en">
<span style="color: #0000ff;"><</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">meta </span><span style="color: #ff0000;">charset</span><span style="color: #0000ff;">="UTF-8"</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>css<span style="color: #0000ff;"></</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">link </span><span style="color: #ff0000;">rel</span><span style="color: #0000ff;">="stylesheet"</span><span style="color: #ff0000;"> href</span><span style="color: #0000ff;">="style.css"</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
<body>
<div>div>
<span style="color: #0000ff;"><</span><span style="color: #800000;">p </span><span style="color: #ff0000;">style</span><span style="color: #0000ff;">="color:#ff7600;"</span><span style="color: #0000ff;">></span>我是段落<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
body>
html>

它会优先执行行内样式，所以在外部样式中含有相同样式时，它是给忽略掉的。

DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>csstitle>
    <style>
    p{
        color: #fff;
    }
    style>
head>
<body>
<div>div>
<span style="color: #0000ff;"><</span><span style="color: #800000;">p </span><span style="color: #ff0000;">style</span><span style="color: #0000ff;">="color:#ff7600;"</span><span style="color: #0000ff;">></span>我是段落<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
body>
html>

从规则中知道这个也一样，内部样式也是被忽略的。

<span style="color: #0000ff;"><!</span><span style="color: #ff00ff;">DOCTYPE html</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">html </span><span style="color: #ff0000;">lang</span><span style="color: #0000ff;">="en"</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">meta </span><span style="color: #ff0000;">charset</span><span style="color: #0000ff;">="UTF-8"</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>css<span style="color: #0000ff;"></</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span><span style="background-color: #f5f5f5; color: #800000;">
    p</span><span style="background-color: #f5f5f5; color: #000000;">{</span><span style="background-color: #f5f5f5; color: #ff0000;">
        color</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> #fff</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
    <span style="background-color: #f5f5f5; color: #000000;">}</span>
    <span style="color: #0000ff;"></</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">link </span><span style="color: #ff0000;">rel</span><span style="color: #0000ff;">="stylesheet"</span><span style="color: #ff0000;"> href</span><span style="color: #0000ff;">="style.css"</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">div</span><span style="color: #0000ff;">></</span><span style="color: #800000;">div</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>我是段落<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">html</span><span style="color: #0000ff;">></span>

根据规则，内部样式优先。

既然样式都会写，那么自己写了很多很多样式代码，然后想找出某处的样式怎么办？一个一个样式看一遍，这个岂不是很耗时，很费神，

既然自己都这样了，那这个代码到了队友那不就是个坑。所以我们是不是可以注释一下他呢，让代码可读性更加强。

CSS注释

<span style="color: #000000;">/*这是头部*/
header{
    color:#fff;
}
/*这是导航*/
nav{}
/*这是主体*/
.container{}

/*这是尾部*/
footer{}</span>

这样是不是可读更强呢。

在HTML中结构可以很复杂，那么我们不可能简单的写个元素选择符吧。

而各种各样方便的选择符，从HTML结构树应运而生。

 选择符

1、通配选择符*

这个是选中全部元素，为他们设置样式。

<span style="color: #0000ff;"><!</span><span style="color: #ff00ff;">DOCTYPE html</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">html </span><span style="color: #ff0000;">lang</span><span style="color: #0000ff;">="en"</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">meta </span><span style="color: #ff0000;">charset</span><span style="color: #0000ff;">="UTF-8"</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>css<span style="color: #0000ff;"></</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span><span style="background-color: #f5f5f5; color: #800000;">
    *</span><span style="background-color: #f5f5f5; color: #000000;">{</span><span style="background-color: #f5f5f5; color: #ff0000;">
        font-size</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 15px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
    <span style="background-color: #f5f5f5; color: #000000;">}</span>
    <span style="color: #0000ff;"></</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">h1</span><span style="color: #0000ff;">></span>标题<span style="color: #0000ff;"></</span><span style="color: #800000;">h1</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>我的段落的兄弟<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>我是段落<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">html</span><span style="color: #0000ff;">></span>

它们的字体都被设置为15像素。

<span style="color: #0000ff;"><!</span><span style="color: #ff00ff;">DOCTYPE html</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">html </span><span style="color: #ff0000;">lang</span><span style="color: #0000ff;">="en"</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">meta </span><span style="color: #ff0000;">charset</span><span style="color: #0000ff;">="UTF-8"</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>css<span style="color: #0000ff;"></</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span><span style="background-color: #f5f5f5; color: #800000;">
    *</span><span style="background-color: #f5f5f5; color: #000000;">{</span><span style="background-color: #f5f5f5; color: #ff0000;">
        font-size</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 15px</span><span style="background-color: #f5f5f5; color: #000000;">;</span><span style="background-color: #f5f5f5; color: #ff0000;">
        font-weight</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> bold</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
    <span style="background-color: #f5f5f5; color: #000000;">}</span>
    <span style="color: #0000ff;"></</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">h1</span><span style="color: #0000ff;">></span>标题<span style="color: #0000ff;"></</span><span style="color: #800000;">h1</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>我的段落的兄弟<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>我是段落<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">html</span><span style="color: #0000ff;">></span>

它们都被加粗了。

2、元素选择符

所谓元素选择符，指以网页中已有的标签名作为名称的选择符。

<span style="color: #000000;">body {}

h1 {}

p {}</span>

3、 群组选择符

除了可以对单个标签进行样式指定外，还可以对一组标签进行相同的样式定义。

使用逗号对选择符进行分隔。对页面中需要使用相同样式的地方，只需写一次样式。

<span style="color: #000000;">p,h1{
        font-size: 15px;
        font-weight: bold;
    }</span>

4、 关系选择符

选择所有被E元素包含的F元素。

<span style="color: #0000ff;"><!</span><span style="color: #ff00ff;">DOCTYPE html</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">html </span><span style="color: #ff0000;">lang</span><span style="color: #0000ff;">="en"</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">meta </span><span style="color: #ff0000;">charset</span><span style="color: #0000ff;">="UTF-8"</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>css<span style="color: #0000ff;"></</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span><span style="background-color: #f5f5f5; color: #800000;">
    p span</span><span style="background-color: #f5f5f5; color: #000000;">{</span><span style="background-color: #f5f5f5; color: #ff0000;">
        color</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> #eee</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
    <span style="background-color: #f5f5f5; color: #000000;">}</span>
    <span style="color: #0000ff;"></</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
    <span style="color: #0000ff;"><</span><span style="color: #800000;">span</span><span style="color: #0000ff;">></span>我是谁？<span style="color: #0000ff;"></</span><span style="color: #800000;">span</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #0000ff;"></</span><span style="color: #800000;">html</span><span style="color: #0000ff;">></span>

 

今日课程知识到此！！！

css.doyoe.com  css参考手册

接下来扩展补充：

特殊性：

每个选择器都有特殊性，而如果一个元素有两个或多个冲突的属性声明，特殊性高的胜出。

选择器的特殊性由选择器本身的组件确定。特殊性值表述为4个部分，如：0,0,0,0. 

一个选择器的具体特殊性如下确定：

对于选择器中给定的各个ID属性值，加0,1,0,0。

对于选择器中给定的各个类属性值、属性选择或伪类，0,0,1，0。

对于选择器中给定的各个元素和伪元素，0,0,0,1。

结合符和通配选择器对特殊性没有任何贡献。

而通配选择器   0,0,0,0.

结合符连零都没有。

例子：

h1{color:red;}   为0,0,0,1 

p em{color：purple}  为0,0,0,2 

.grape{color:purple}  为0,0,1,0

p.b e.a{color:red; }   0,0,2,2

#aa{color:red;}    0,1,0,0

div#aa *[href]{color:red;}  0,1,1,1

而第一个0是为行内样式准备的，因为越前面，代表优先级越高，假如非零数字位置一样，那么先比较前面的数字的大小，

然后再往下比较，直到数字不相对，取数字大那个的优先级高。

重要声明 !important   ,就是把你所需要的声明标出来，它的优先级最高，不过它要放在声明的值的最后。 

继承：

继承的特殊性连零都没有，就是没有特殊性；

这个0特殊性有零与无特殊性有很大的区别，就是0特殊性的选择器可以为后代加样式，

而继承虽然也有给后代加样式，但有限制的，只有有继承能力的才能加到后代元素中，如color等，而margin、padding和border这些属性都不会加到后代里。

相同权重的，按顺序比较，顺序越下他的优先级最高。

较高特殊性强于较低特殊性

所以伪类声明顺序：link-visited-hover-active

LVHA（简写）

当:visited在他们之后时，由于权重一样，所以会看他们的顺序，而:visited在他们之后会胜出。

当不是写统一属性就不会出现这种问题。所以写同一种属性时要注意 ！！！！