CSS introduction learning notes + cases

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Introduction to CSS

1, CSS introduction

1. What is CSS

CSS: Cascading Style Sheet

Is a set of style setting rules that control the appearance style of a page

2. Why CSS

Realize the separation of content and style, which is convenient for team development

Style reuse is convenient for the later maintenance of the website

The precise control of the page makes the page more exquisite

3. CSS function

Page beautification

Layout and positioning

2, Basic usage

1. CSS syntax

<head>
	<style>
		selector{
			Attribute name: attribute value;
			Attribute name: attribute value;
		}
	</style>
</head>

Selector: object (thing) to decorate
Attribute name: which attribute (style) decorates the object
Attribute value: the value of the style
Document
CSS from entry to mastery

Speaker: hector

Example:

2. CSS application mode

Also known as CSS reference method, there are three methods: internal style, inline style and external style

2.1 internal style

Also known as inline style, it is defined in the page header by the style tag

Works on all labels in the current page that match the style selector

2.2 inline style

Also known as embedded style, it is defined using the style attribute of HTML tags

Works only on labels that set the style attribute

2.3 external style

Use a separate CSS file definition, and then use the link tag or @ import instruction to introduce it in the page

Use the link tag to link external style files
```
<link rel="stylesheet" type="text/css" href="CSS Path to the style file">
```
Tip: the type attribute can be omitted
@The import directive imports an external style file
```
<style>
	@import "CSS Style file path";
	@import url(CSS Style file path);
</style>
```
Document
welcome to CSS!

Welcome to CSS class!

WEB front Engineer

JAVA Development Engineer

hey

ha-ha

Example:

3, Selector

1. Base selector

1.1 label selector

Also known as an element selector, it uses an HTML tag as the name of the selector

The label name is used as the basis for style application

Type 1.2 selector

Use a custom name to Number as the prefix, and then call the class selector through the class attribute of the HTML tag

The class attribute of the label is used as the basis for style application

matters needing attention:

Cannot add when calling number
When multiple class selectors are called at the same time, they are separated by spaces
Class selector names cannot begin with a number

1.3 ID selector

Use a custom name with # as the prefix, and then match the name through the id attribute of the HTML tag

The id attribute of the tag is used as the basis for style application, which is a one-to-one relationship

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
		p{
			color:red;
			font-size:20px;
		}
		h2{
			color:yellow;
		}
		.hello{
			background: #cccccc;
		}
		.world{
			font-weight:bold;
		}
		#haha{
			color:blue;
		}
	</style>
</head>
<body>
	<p>welcome to css!</p>
	<p>hello world!</p>
	<h2>WEB Front end development</h2>
	<h3>Java development</h3>
	<hr>
	<p class="hello">welcome to css!</p>
	<p>hello world!</p>
	<h2>WEB Front end development</h2>
	<h3>Java development</h3>
	<div class="hello">be the speaker: Hector</div>
	<div class="world">be the speaker: Hector</div>
	<hr>
	<h1 id="haha">ha-ha</h1>
</body>
</html>

Example:

2. Complex selector

2.1 compound selector

Label selectors and class selectors, label selectors and ID selectors are used together

Two conditions must be met to apply a style

2.2 combined selector

Also known as collective declaration

Declare multiple selectors with the same style together, separated by commas

2.3 nested selectors

Set selectors inside a selector, separated by spaces

Only the label corresponding to the selector that meets the innermost level of the hierarchical relationship will be applied with the style

Note: when using spaces, it does not distinguish between father and son or offspring. When using > added in CSS3, it must be a parent-child relationship

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
		/* 1.Label selector and class selector are used together -- compound selector */
		h1.aaa{
			color:red;
		}
		/* 1.Tag selector and ID selector are used together -- compound selector */
		p#bbb{
			color:blue;
		}
		/* 2.Combination selector */
		h1,p,div,span,.ccc{
			font-size:30px;
		}
		div{
			background:violet;
		}
		.ccc{
			font-weight:bold;
		}
		/* 3.Nested selector */
		/* div p{
			color:green;
			text-decoration:underline;
		} */
		div>p{
			color:green;
			text-decoration:underline;
		}
		div h3.ddd{
			color:red;
		}
	</style>
</head>
<body>
	<!-- Demand: just want to decorate class Attribute is aaa of h1 label -->
	<h1 class="aaa">welcome</h1>
	<h4 class="aaa">css</h4>
	<h1>hello</h1>
	<hr>
	<!-- I want to decorate ID Attribute is bbb of p label -->
	<p id="bbb">world</p >
	<p>html</p>
	<h1 id="bbb">Speaker: Jiji</h1>
	<hr>
	<!-- to h1,p,div,span Set the font size of the content in the label to 30 px -->
	<h1>hello</h1>
	<p>CSS</p>
	<div>WEB development</div>
	<span class="ccc">JAVA development</span>
	<hr>
	<!-- Requirements: modification div Internal p label -->
	<div>
		<p>div Internal p label</p>
		<h3>div Internal h3 label</h3>
	</div>
	<hr>
	<div>
		<h3>
			<p>div Internal h3 Internal p label</p>
		</h3>
	</div>
	<hr>
	<!-- Requirements: modification div Internal class by ddd Label of -->
	<div>
		<p>div Internal p</p>
		<h3 class="ddd">div Internal h3</h3>
		<p class="ddd">PPPP</p>
	</div>
	<h3 class="ddd">h3h3h3</h3>
</body>
</html>

Example:

2.4 pseudo class selector

Different styles are displayed according to different states, which are generally used for labels

Four states:

: link links not visited
: visited visited links
: hover the mouse over the connection, that is, move it over the connection
: active the selected link is activated

Note: the default hyperlink is blue and underlined

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Pseudo class selector</title>
	<style>
		/*a:link{
			font-size: 12px;
			color:black;
			text-decoration: none;
		}
		a:visited{
			font-size: 15px;
			color:;
		}
		a:hover{
			font-size: 20px;
			color:blue;
		}
		a:active{
			font-size: 40px;
			color:green;
		}*/
		a:link,a:visited{
			color:#666666;
			font-size: 13px;
			text-decoration: none;
		}
		a:hover,a:active{
			color:#ff7300;
			text-decoration: underline;
		}
		/*Ordinary tags can also use pseudo class selectors*/
		p:hover{
			color:red;
		}
		p:active{
			color:blue;
		}
	</style>
</head>
<body>
	<a href="Complex selector.html">Complex selector.html</a>
	<p>CSS From introduction to mastery!</p>
</body>
</html>

Example:

2.5 pseudo element selector

: first letter is the style of the first character
: first line adds a style to the first line
: before the content added at the front of the element content needs to be used in conjunction with the content attribute
: after: the content added on the last side of the element content needs to be used in conjunction with the content attribute
Document
hello world!

hello world!
welcome to css!

Example:

3. Selector priority

3.1 priority

Inline style > ID selector > class selector > label selector

Reason: first load the label selector, then the class selector, then the ID selector, and finally the inline style

Later loading overwrites the style with the same name that was loaded first

3.2 loading order of internal and external styles

Proximity principle

Reason: it is loaded in sequence according to the writing order. On the premise of the same priority, the later loaded will overwrite the style with the same name loaded first, so the closer it is

More priority

3.3 !important

Can use! important gives a style the highest priority

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<link rel="stylesheet" type="text/css" href="style/world.css">

	<style>
		div{
			font-size:20px;
		}
		.hello{
			font-weight:bold;
			color:blue;
		}
		#world{
			text-decoration: underline;
			color:green;
		}
		p{
			color:red;
		}
	</style>
</head>
<body>
	<div class="hello" id="world" style="color:#Ff7300 "> CSS from getting started to mastering < / div >
<p>Speaker: Jiji</p>
</body>
</html>

Example:

4, Common CSS properties

1. Font attribute

Set font related styles

attribute

meaning

explain

font-size

Size, size

Multiple units can be used

font-weight

thickness

font-family

typeface

font-style

style

font

Abbreviation

1.1 font-size

Value:

Inherited. The font size (default value) is inherited from the parent tag by default. The default value of all CSS properties is inherited
px pixel
%Percentage, relative to the font size of the parent label
em multiple, a multiple of the font size of the parent label

The root font size of HTML elements is also called the default font size of PX

1.2 font-weight

Value:

Normal normal (default)
Bold bold
Customize 400 normal 700 bold

1.3 font-family

The specified font is required to be installed in the system

It is generally recommended to write three fonts: preferred, secondary and standby. Separated by commas

1.4 font-style

Value:

Normal normal
italic Italic

1.5 font

Abbreviated attribute: font: font style|font weight|font size|font family

It must be written in this order

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
		div{
			font-size: 30px;
		}
		p{
			/*font-size: 20px;*/
			font-size: 80%;
		}
		.hello{
			font-size: 2em;
		}
		body{
			font-size: 62.5%;
		}
		ul li{
			/*font-size: 30px;
			font-weight: bold;
			font-family: Chinese Xingkai, Song typeface, boldface;
			font-style: italic;*/
			font: italic bold 30px Microsoft YaHei ;
		}
	</style>
</head>
<body>
	<p>
		CSS From introduction to mastery!
		<span>Speaker: Jiji</span>
	</p>
	<span>Speaker: Jiji</span>
	<hr>

	<div>
		my DIV
		<p>
			CSS From introduction to mastery
			<span>Speaker: Jiji</span>
		</p>
	</div>
	<hr>

	<span class="hello">Speaker: Jiji</span>
	<hr>

	<ul>
		<li>
			hey
		</li>
	</ul>
</body>
</html>

Example:

2. Text attributes

attribute

meaning

explain

color

colour

line-height

Row height

Height between rows

text-align

Horizontal alignment

Values: left, center, right

vertical-align

Vertical alignment

Values: top, middle and bottom can be used for image and text alignment

text-indent

text-decoration

Text modification

Values: under line, over line, line through

text-transform

Letter case conversion

Values: lowercase, uppercase, capitalize

letter-spacing

Character spacing

word-spacing

Word spacing

Valid for English only

white-space

Processing method of blank

Whether to wrap the text after it exceeds the value: nowrap

2.1 color

Value, written in four ways:

Color name: use English words
RGB value in hexadecimal: #RRGGBB

Abbreviations can be used in specific cases

#FFFFFF--->#FFF white 
#000000--->#000 black 
#FF0000--->#F00 red 
#00FF00--->#0F0 green 
#0000FF--->#00F blue 
#CCCCCC--->#CCC grey 
#Ff7300 --- > cannot be abbreviated

Note: case insensitive

RGB function: rgb(red,green,blue)

Value range of each color, [0255]

rgb(255,0,0)----->red 
rgb(0,255,0)----->green 
rgb(0,0,255)----->blue

rgba function: rbga(red,green,blue,alpha)

Transparency can be set. alpha value range: [0,1] 0 means fully transparent and 1 means fully opaque

rgba(255,0,0,1)----->Pure red 
rgba(255,0,0,0.5)---->Red translucent

Document

welcome to css!

<img src="../qq.png" alt="" width="15%">
HTML and CSS Is it simple?
<hr>


<div>&nbsp;&nbsp;welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS</div>
<hr>
<div>welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS</div>
<hr>

<span>hello world</span>
<hr>

<h3>welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS welcome to CSS</h3>
<hr>

Example:

3. Background attribute

attribute

meaning

explain

background-color

background color

background-image

Background picture

background-repeat

Repetition mode of background picture

background-position

Display position of background picture

background-attachment

Whether the background picture follows the scroll

background

Abbreviation

3.1 background-color

Value: transparent

3.2 background-image

The path of the picture must be specified by url()
If relative paths are used in css style files, they are relative to css files, not html files

3.3 background-repeat

Values: repeat (default), repeat-x, repeat-y, no repeat

3.4 background-position

The default background image is displayed in the upper left corner

Value:

Keywords: top, bottom, left, right, center
Coordinates: the upper left corner is the (0,0) coordinate, the right is the x positive direction, and the down is the y positive direction

CSS Sprite, or CSS Sprites, also known as CSS Sprites, is a CSS image merging technology

Meaning: integrate many very small icons / pictures in the web page into a large picture. When visiting the page, you only need to download them once, which can reduce the number of visits

Number of servers to improve performance

Principle: use background position to locate the background, and use coordinates to accurately locate the position of the background picture

3.5 background-attachment

Values: scroll (default), fixed

3.6 background

Abbreviated attribute: BACKGROUND: background color | background image | background repeat | background position

Separated by spaces, there is no requirement for writing order

4. List properties

attribute

meaning

explain

list-style-type

Set tag before list

list-style-image

Use the image as a marker before the list

list-style-position

Set the location of the marker

Values: outside (default), inside

list-style

Abbreviation

4.1 list-style-type

Values: none, disc, circle, square, decimal

At this time, it is no longer necessary to distinguish between sequential list and unordered list. Just set the mark in front of the list

4.2 list-style

Abbreviated attribute: list style: list style type|list style image|list style position

The writing order is not required

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
/* 		li{
			list-style-type:decimal;
		} */	
		.first{
			list-style-type:circle;
		}
		.second{
			list-style-image:url(../images/male.gif);
		}
		.third{
			list-style-type:circle;
			list-style-position:inside;
		}
		.fourth{
			list-style:circle url(../images/female.gif)inside;
			/* list-style:none; */
		}
		.nav{
			/* list-style:none;
			float:left; */
		}
		.nav li{
			list-style:none;
			float:left;
			width:70px;
		}
	</style>
</head>
<body>
	<ul>
		<li class="first">hello</li>
		<li class="second">hello</li>
		<li class="third">hello</li>
		<li class="fourth">hello</li>
	</ul>
	<hr>
	<nav>
		<ul class="nav">
			<li>Journalism</li>
			<li>novel</li>
			<li>Eretti</li>
			<li>Politics</li>
			<li>study</li>
		</ul>
	</nav>
</body>
</html>

Example:

5. Table attributes

Border collapse: whether adjacent borders in the table are merged (collapsed) into a single border

Value: separated (default) collapse

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
		table{
			width:500px;
			border:1px solid blue;
			border-collapse:collapse;
		}
		td{
			border:1px solid blue;
		}
	</style>
</head>
<body>
	<!-- table>(tr>td{td$}*5)*4 -->
	<table cellspacing="0px"cellpadding="0px">
		<tr>
			<td>bbb</td>
			<td>aaa</td>
			<td>aaa</td>
			<td>td4</td>
			<td>td5</td>
		</tr>
		<tr>
			<td>aaa</td>
			<td>aaa</td>
			<td>bbb</td>
			<td>td4</td>
			<td>td5</td>
		</tr>
		<tr>
			<td>td1</td>
			<td>td2</td>
			<td>td3</td>
			<td>td4</td>
			<td>td5</td>
		</tr>
		<tr>
			<td>td1</td>
			<td>td2</td>
			<td>td3</td>
			<td>td4</td>
			<td>td5</td>
		</tr>
	</table>
</body>
</html>

Example:

6. Use LiveReload

It can refresh the browser in real time when saving the page file

Steps:

Installing the LiveReload extension in Chrome

Unzip livereload – > Chrome browser select "..." – > more tools – > extensions – > open "developer mode" – > load the unzipped extensions – > select the folder name livereload

Tip: "allow" to read and change retained information on all websites
Install the livereload plug-in in sublime

Unzip "livereload. Rar ----- used in sublime" into the plug-in directory packages / in sublime
Configure the LiveReload plug-in in Sublime

preference–>packages settings–>livereload–>settings-default
```
{ 
	"enabled_plugins": [ 
	"SimpleReloadPlugin" 
	"SimpleRefresh"
	] 
}
```
Enable LiveReload in browser

First open the page to be accessed by the browser, and then click the black circle on the right side of the browser address bar. When the small circle in the center changes to a solid circle, it indicates that it is enabled
Enable liveReload in sublime

Press ctrl+shift+P – > search for livereload and select enable – > search for simple reload: select enable

5, Box model

1. Introduction

The box model is the basis of web page layout. All elements in the page are regarded as a box. The box contains the following attributes:

width
Height height
Border border
padding inner margin
Margin margin

2. Box model

2.1 border

Represents the border of the box

It is divided into four directions:

top, right, bottom, left
border-top,border-right,border-bottom,border-left

Each border contains three styles:

border-top-color,border-top-width,border-top-style
border-right-color,border-right-width,border-right-style
border-bottom-color,border-bottom-width,border-bottom-style
border-left-color,border-left-width,border-left-style

Value of style:

Solid solid line, dashed dotted line, dotted dotted line, double double double line, inset embedded 3D line, outlet embedded 3D line

Abbreviation, three ways:

Abbreviation by direction:

border-top,border-right,border-bottom,border-left

Writing order:

border order: width style color
By style:

border-color,border-width,border-style

Writing order:

border style: top right bottom left

It must be written clockwise and can be abbreviated:
- border-width:2px;---------> The width of the four borders is 2px
- border-width:1px 2px;
- border-width:1px 2px 4px;
Rule: if omitted, it is considered that the top and bottom are the same and the left and right are the same
Final abbreviation:

If the four border styles are exactly the same, border:width style color;

2.2 padding

Represents the inner margin of the box, that is, the distance between the content and the border

It can also be divided into four directions, which can also be abbreviated (clockwise, the default is the same up and down, the same left and right)

Note: in case of conflict between top and bottom, the above shall prevail; in case of conflict between left and right, the left shall prevail

2.3 margin

Represents the outer distance of the box, that is, the distance between the box and the box

It can also be divided into four directions, which can also be abbreviated (clockwise, the default is the same up and down, the same left and right)

Center alignment:

/* Horizontal center of element */ 
/* 1.Horizontal centering of block level elements */ 
    margin:0 auto; 
    /* Tip: block level elements must have a width specified */
    /* 2.Horizontal center of text */ 
    text-align:center; 
    /* 3.Center vertically and set the height and line height to the same */ 
    height:100px; 
    line-height:100px;


<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
		p{
			width:250px;
			background:#ccc;
		}
		.first{
			/* border-top-color:red;
			border-top-width:1px;
			border-top-style:solid;
			border-right-color:blue;
			border-right-width:2px;
			border-right-style:dotted;
			border-bottom-color:green;
			border-bottom-width:4px;
			border-bottom-style:dashed;
			border-left-color:gray;
			border-left-width:6px;
			border-left-style:double; */

			/* border-top:1px solid red;
			border-bottom:2px dashed blue; */
			
			/* border-color:red yellow green;
			border-width:1px 2px 4px 6px;
			border-style:solid dashed dotted solid; */

			border:1px solid red;
			padding:20px;
			margin:10px;
		}
		.second{
			/* padding-top:5px;
			padding-left:3px;
			padding-bottom:10px;
			padding-right:8px; */

			/* padding:1px 2px 4px 6px; */

			padding:5px;
		}
		.third{
			/* margin-top:50px;
			margin-left:30px; */

			/* margin:10px 20px; */

			/* Centering of elements */
			/* 1.Block level elements are horizontally centered */
			margin:auto;
			/* 2.Text centered horizontally */
			text-align:center;
			/* 3.Center the text vertically and set the height and line height to be the same */
			height:100px;
			line-height:100px;
		}
	</style>
</head>
<body>
	<p class="first">nihao</p>
	<p class="second">hello</p>
	<p class="third">welcome</p>
</body>
</html>

Example:

3. Others

3.1 space occupied by elements

The actual space occupied by the elements in the page

Width = width + padding + border + margin
Height = height + padding + border + margin

3.2 box attribute default value

The default values of box attributes of different labels may be different and need to be set by yourself

body,ul,ol,dl,li,p,h1,h2,h3,h4,h5,h6,form{
	margin:0; 
	padding:0; 
}


<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
	/* body The default margin is not 0 */
		body{
			margin:0;
			padding:0;
		}
	/* p The default margin is not 0 */
		p{
			margin:0;
		}
		ul{
			list-style:none;
			margin:0;
			padding:0;
		}
		body,ul,ol,dl,li,p,h1,h2,h3,h4,h5,h6,form{
			margin:0;
			padding:0;
		}
	</style>
</head>
<body>
	welcome to css!
	<p>hello world</p>
	<!-- ul>li{hello$}*3 -->
	<ul>
		<li>hello1</li>
		<li>hello2</li>
		<li>hello3</li>
	</ul>
</body>
</html>

Example:

3.3 consolidation of outer margins

Also known as outer margin folding, it refers to that when two block level elements meet the vertical outer margin, they will be merged into one outer margin, and the merged outer margin

The outer margin value is the larger one

There are two situations:

When an element appears on top of another element, the lower margin of the first element is merged with the upper margin of the second element
When an element is contained in another element and there is no inner margin or border to separate the outer margin, the upper and outer margins of the two elements are merged

The advantages of the combination of outer margins make the typesetting look more beautiful visually

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
		div{
			width:50px;
			height:50px;
			background:#cccccc;
		}
		.div1{
			margin-bottom:20px;
		}
		.div2{
			margin-top:30px;
		}
		.div3{
			width:100px;
			height:100px;
			background:blue;
			margin-top:20px;
			/* padding:2px;
 */			/* border:1px solid red; */
		}
		.div4{
			margin-top:30px;
		}
		p{
			margin:20px 0;
		}
	</style>
</head>
<body>
	<div class="div1">div1</div>
	<div class="div2">div2</div>
	<hr>

	<div class="div3">
		<div class="div4"></div>
	</div>
	<hr>
	<p>p1</p>
	<p>p2</p>
	<p>p3</p>
	<p>p4</p>
	<p>p5</p>
	<p>p6</p>
	<p>p7</p>
</body>
</html>

Example:

6, Positioning mode

1. Introduction

There are four ways to locate elements through the position attribute

Common values:

Value

meaning

explain

static

Default value

Display according to regular document flow

relative

Relative positioning

Positioning relative to the original position of the label

absolute

Absolute positioning

Positioning of the parent tag relative to the first non static positioning

fixed

Fixed positioning

Positioning relative to browser window

After setting the positioning method, set the positioning attributes (offset): top, bottom, left, right

2. Relative positioning

First set the position attribute of the element to relative, and then set the offset

3. Absolute positioning

First set the parent tag to non static positioning, then set the position attribute of the element to absolute, and finally set the offset

be careful:

In general, the parent tag is set to non static positioning
If the parent tag is not non static, it is positioned relative to the browser window
When the element is set to absolute positioning, the element will float to the top of the page

4. Fixed positioning

First set the position attribute of the element to fixed, and then set the offset

When the element is set to fixed positioning, the element will float above the face

5.z-index

After setting the element positioning method, the element will float at the top of the page. At this time, you can set the priority through the z-index attribute to control the stacking order of elements

The value is a number. The higher the value, the higher the priority. The default is auto(0 for most browsers)

Note: the z-index attribute can only be set for non static elements

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
		#container{
			width:800px;
			border:1px solid #000000;
			position:relative;
		}
		.div1,.div2,.div3,.div4{
			width:100px;
			height:50px;
		}
		.div1{
			background:red;
			position:relative;/* Relative positioning */
			top:20px;
			left:50px;
			z-index:-5;
		}
		.div2{
			background:blue;
			position:absolute;
			left:100px;
			bottom:50px;
			z-index:-8;
		}
		.div3{
			background:green;
			position:fixed;
			bottom:50px;
			left:100px;
		}
		.div4{
			background:cyan;
		}
	</style>
</head>
<body>
	<div id="container">
		<div class="div1">div1</div>
		<div class="div2">div2</div>
		<div class="div3">div3</div>
		<div class="div4">div4</div>
	</div>
</body>
</html>

Example:

7, Other CSS properties

1. Floating and clearing

1.1 floating attributes

The floating of elements is realized through the float attribute, which can make the block level elements break away from the regular document flow, move left or right, and display on the same line,

If one line cannot be displayed, it will be wrapped

Common values:

left float
Right float right
none does not float, default

After setting the float attribute, the element will float on the upper layer of the page. At this time, the parent container cannot calculate its own size. If we still want to display the parent container, we usually add an empty div with the float attribute cleared at the end

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
		#container{
			/* width:800px; */
			border:1px solid #000000;
		}
		.div1,.div2,.div3,.div4{
			width:100px;
			height:50px;
		}
		.div1{
			background:red;
			float:left;
		}
		.div2{
			background:blue;
			float:left;
		}
		.div3{
			background:green;
			float:left;
		}
		.div4{
			background:cyan;
			float:left;
		}
		.clr{
			clear:left;
		}
	</style>
</head>
<body>
	<div id="container">
		<div class="div1">div1</div>
		<div class="div2">div2</div>
		<div class="div3">div3</div>
		<div class="div4">div4</div>
		<div class="clr"></div>
	</div>
	aaa
</body>
</html>

Example:

1.2 clear attributes

Clear is achieved through the clear attribute, which side of the element is not allowed to have floating elements

Common values:

Floating elements are not allowed on the left
Floating elements are not allowed on the right
Floating elements are not allowed on both sides of the both
none allows floating elements on both sides, default value

Conclusion:

For non floating elements, clear can be set on both sides (common)
For floating elements, you can only set which side to clear
Document

welcome to css

Example:

2. Display and hiding of elements

2.1 display

Set whether the element is displayed and whether a row is exclusive through the display attribute

Common values:

Value

meaning

explain

none

Do not show

inline

Displayed as inline elements, the default value of row level elements

Change a block level element into a row level element and no longer monopolize a row

block

Displayed as a block level element, the default value of the block level element

Change row level elements into block level elements and monopolize one row

inline-block

Displays as inline elements, but width and height can be set

Width and height can be set on the basis of inline

be careful:

The width and height of row level elements cannot be set. You can set display: inline block for row level elements, and then you can set the width and height

2.2 visibility

You can also set the display and hiding of elements through the visibility attribute

Common attributes:

Value

meaning

explain

visible

display

hidden

hide

2.3 differences

When display is hidden, it no longer occupies the space in the page, and the subsequent elements will occupy their positions
When visibility is hidden, it will occupy the space in the page, and the position will remain in the page, but it will not be displayed
Document
div1
span1 hehe
hello

world

Example:

3. Profile attributes

3.1 introduction

Outline is used to draw an outline around the element, which is located on the periphery of the border and can highlight the element

3.2 basic usage

Common attributes:

Outline width: outline width
Outline color: outline color
Outline style: outline style
outline abbreviation

In the browser, when you click the mouse or use the TAB key to focus a form or link, the element will have an outline

Advantages: it can improve the user experience of using forms

Disadvantages: sometimes it will affect the appearance

3.3 difference between outline and border

border can be applied to all html elements, while outline is mainly used for form elements and hyperlink elements
When the element gets focus, the outline effect will appear automatically, and when it loses focus, it will disappear automatically, which is the default behavior of the browser
outline does not affect the size and position of elements, while border does
Document welcome to CSS user name: CSS Email:
div

Example:

4. Other attributes

4.1 width height correlation

Max width: sets the maximum width of the element
Max height: sets the maximum height of the element
Min width sets the minimum width of the element
Min height sets the minimum height of the element

4.2 overflow attribute

How to deal with the overflow of element content

Common values:

Visible overflow is visible. It is displayed outside the element. The default value is
hidden overflow part is not visible (common)
scroll always appears regardless of overflow
The scroll bar appears automatically when auto overflows

4.3 cursor attribute

Used to set the shape of the cursor

Common attributes:

Default is the default cursor, usually an arrow
When the cursor is in the shape of hand, the hyperlink is generally displayed in the shape of hand
move means movable
Text indicates text
Wait indicates that the program is busy and needs to wait
hep means help
Document
welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css

welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css welcome to css
Cursor shape

Example:

8, Page layout

1. Introduction

Common page layouts:

Table layout
div layout

2. Table layout

2.1 introduction

It is not suitable for complex layout, but only for simple and regular structure

The positioning is relatively accurate and has nothing to do with the browser. It is suitable for simple separation

2.2 usage

table common style properties

Border sets the border around the table
Border spacing sets the distance between cells (equivalent to the cellspacing attribute in the table label, i.e. spacing)
Whether the adjacent borders in the border collapse table are merged. The values are seprate and collapse

th/td common style attributes:

Border sets the border for the cell
padding sets the inner margin of the cell (equivalent to the cellpadding attribute in the table tag, margin)
Document
th1 th2 th3 th4
td1 td2 td3 td4
td1 td2 td3 td4
td1 td2 td3 td4
td1 td2 td3 td4
td1 td2 td3 td4
td1 td2 td3 td4

th1	th2	th3	th4
td1	td2	td3	td4
td1	td2	td3	td4
td1	td2	td3	td4
td1	td2	td3	td4
td1	td2	td3	td4
td1	td2	td3	td4

Example:

3.div layout

The positioning is absolutely accurate and flexible, which is suitable for complex layout

3.1 simple layout

Two forms:

1-1-1 layout

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<link rel="stylesheet" href="css/style1.css">
</head>
<body>
	<div id="container">
		<header class="header">
			header
		</header>
		<article class="main">
			main
		</article>
		<footer class="footer">
			footer
		</footer>
	</div>
</body>
</html>

Example:

1-2 / 3-1 layout

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	 <link rel="stylesheet" href="css/style2.css"> 
</head>
<body>
	<div id="container">
		<header class="header">
			herder
		</header>
		<article class="wrapper">
			<section>
				main
			</section>
			<aside>
				right aside
			</aside>
		</article>
		<footer class="footer">
			footer
		</footer>
	</div>
</body>
</html>

Example:

3.2 grail layout

Page structure, the width of sidebars on both sides is fixed, the middle subject can be adaptive within a certain range, and the subject is loaded first

In general, to prevent page scaling from affecting browsing, a minimum width will be set for the page

<!DOCTYPE html>
<html lang="en"> 
<head>
	<meta charset="UTF-8"> 
	<title>Document</title> 
	<link rel="stylesheet" href="css/style4.css"> 
</head> 
<body>
	<div id="container">
		<header class="header"> 
            header 
        </header> 
		<article class="wrapper"> 
			<section class="main">
				main
			</section>
			<aside class="left"> 
				left
			</aside>  
			<aside class="right"> 
				right
			</aside> 
		</article>
		<footer class="footer"> 
            footer 
        </footer>  
    </div>
</body> 
</html>

Example:

3.3 double wing layout

UED (user experience design) team from taobao

The effect of the double wing layout and the Holy Grail layout is the same, but the ideas are different

The difference between the Grail layout and the twin wing layout

The twin wing layout creates one div more than the Grail layout

The double flying wing layout does not need to set the inner margin, relative positioning, or offset

The double wing layout uses margin and the Holy Grail layout uses padding

In the actual development, it is recommended to use the flex elastic box layout newly added in CSS3 to simplify the layout

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
    <title>Document</title> 
    <link rel="stylesheet" href="css/style5.css">
</head>
<body>
    <div id="container">
        <header class="header">
            header 
        </header> 
        <article class="wrapper">
            <section class="main">
                <div class="main-wrapper">
                    main 
                </div> 
            </section>
            <aside class="left">
                left aside
            </aside>
            <aside class="right">
                right aside 
            </aside>
        </article>
        <footer class="footer">
            footer 
        </footer> 
    </div>
    </body>
</html>

Example:

enclosure: https://share.weiyun.com/6GKjzjpt

Keywords: Javascript Front-end html

Added by xiaix on Fri, 25 Feb 2022 03:02:50 +0200

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Programming VIP

CSS introduction learning notes + cases

Introduction to CSS

1, CSS introduction

1. What is CSS

2. Why CSS

3. CSS function

2, Basic usage

1. CSS syntax

Speaker: hector

2. CSS application mode

2.1 internal style

2.2 inline style

2.3 external style

WEB front Engineer

JAVA Development Engineer

3, Selector

1. Base selector

1.1 label selector

Type 1.2 selector

1.3 ID selector

2. Complex selector

2.1 compound selector

2.2 combined selector

2.3 nested selectors

2.4 pseudo class selector

2.5 pseudo element selector

3. Selector priority

3.1 priority

3.2 loading order of internal and external styles

3.3 !important

4, Common CSS properties

1. Font attribute

1.1 font-size

1.2 font-weight

1.3 font-family

1.4 font-style

1.5 font

2. Text attributes

2.1 color

3. Background attribute

3.1 background-color

3.2 background-image

3.3 background-repeat

3.4 background-position

3.5 background-attachment

3.6 background

4. List properties

4.1 list-style-type

4.2 list-style

5. Table attributes

6. Use LiveReload

5, Box model

1. Introduction

2. Box model

2.1 border

2.2 padding

2.3 margin

3. Others

3.1 space occupied by elements

3.2 box attribute default value

3.3 consolidation of outer margins

6, Positioning mode

1. Introduction

2. Relative positioning

3. Absolute positioning

4. Fixed positioning

5.z-index

7, Other CSS properties

1. Floating and clearing

1.1 floating attributes

1.2 clear attributes

2. Display and hiding of elements

2.1 display

2.2 visibility

2.3 differences

3. Profile attributes

3.1 introduction

3.2 basic usage

3.3 difference between outline and border

th1	th2	th3	th4
td1	td2	td3	td4
td1	td2	td3	td4
td1	td2	td3	td4
td1	td2	td3	td4
td1	td2	td3	td4
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