Table of contents
1.1 Common layout methods of web pages
1.2 Common Application Scenarios for Positioning
2.1 First experience of positioning
8.2 Changing the hierarchy of positioned elements
3.2 Common applications of frame rounded corners
4.1 The display effect of the overflow part
5.1 The element itself is hidden
5.2 Element display hide switch case
(Extended) The overall transparency of the element
(Expansion) Skills of drawing triangles with CSS (interview questions)
1. Positioning
1.1 Common layout methods of web pages
1. Standard stream
(1) Block-level elements occupy a single line → vertical layout
(2) Inline elements/inline block elements display multiple items in one row → horizontal layout
2. float
It can make the block-level elements in the original vertical layout into a horizontal layout, breaking away from the standard flow
3. Positioning
(1) Elements can be freely placed anywhere on the web page
(2) Generally used for stacking between boxes
1.2 Common Application Scenarios for Positioning
1. It can solve the cascading problem between boxes
• The positioned element has the highest level and can be stacked on top of other boxes
2. The box can always be fixed at a certain position on the screen (the header part of JD.com)
2.1 First experience of positioning
Requirements: There are two boxes on the page, which require to complete the effect of the picture, how can it be completed?
➢ For the cascading problem between boxes, it is recommended to use positioning
2.2 Using positioning
1. Set the positioning method
➢ Property name: position
➢ Common attribute values:
| Targeting | attribute value |
| static positioning | static |
| relative positioning | relative |
| absolute positioning | absolute |
| fixed positioning | fixed |
2. Set the offset value
➢ Offset value setting is divided into two directions, choose one for horizontal and vertical direction
➢ The principle of selection is generally the principle of proximity (whichever is closest)
| direction | attribute name | attribute value | meaning |
| level | left | number+px | distance from left |
| level | right | number+px | distance to the right |
| vertical | top | number+px | distance from top |
| vertical | bottom | number+px | distance from bottom |
3.1 Static positioning
➢ Introduction : Static positioning is the default value, which is the standard stream previously known.
➢ Code: position: static
➢ Notes:
1. Static positioning is the previous standard flow, which cannot be moved through the orientation attribute
2. The positioning mentioned later does not include static positioning, and generally refers to the latter types: relative, absolute, and fixed
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
/* css书写: 1. 定位 / 浮动 / display ; 2. 盒子模型; 3. 文字属性 */
.box {
/* 静态定位, 默认值, 标准流 */
position: static;
left: 100px;
top: 200px;
width: 200px;
height: 200px;
background-color: pink;
}
</style>
</head>
<body>
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<div class="box">box</div>
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</body>
</html>4.1 Relative positioning
➢ Introduction: Narcissistic positioning, moving relative to one's previous position
➢ Code:
position:relative➢Features : _
1. It needs to cooperate with the orientation attribute to realize the movement
2. Move relative to your original position
3. Occupy a position on the page → no off-label
➢ Application scenarios:
1. Cooperate with the absolute positioning group CP (son and father)
2. For small-scale movement
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
/* 如果left和right都有, 以left为准; top和bottom都有以top 为准 */
/* css书写: 1. 定位 / 浮动 / display ; 2. 盒子模型; 3. 文字属性 */
.box {
position: relative;
right: 200px;
bottom: 400px;
left: 100px;
top: 200px;
/*
1. 占有原来的位置
2. 仍然具体标签原有的显示模式特点
3. 改变位置参照自己原来的位置
*/
width: 200px;
height: 200px;
background-color: pink;
}
</style>
</head>
<body>
<p>测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位</p>
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<div class="box">box</div>
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<p>测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位</p>
<p>测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位</p>
</body>
</html>5.1 Absolute positioning
➢ Introduction: Competitive positioning, positioning and moving relative to the parent element that is not statically positioned
➢ Code:
position:absoulte➢ Features:
1. It needs to cooperate with the orientation attribute to realize the movement
2. By default, it moves relative to the visible area of the browser
3. Does not occupy a place on the page → has been unlabeled
➢ Application scenario: Cooperate with the absolute positioning group CP (son and father)
➢ Relative to whom do absolutely positioned elements move?
1. There is no positioning in the ancestor element → the default is to move relative to the browser
2. Positioned in ancestor → move relative to nearest positioned ancestor
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
/* css书写: 1. 定位 / 浮动 / display ; 2. 盒子模型; 3. 文字属性 */
.box {
/* 绝对定位:
先找已经定位的父级, 如果有这样的父级就以这个父级为参照物进行定位;
有父级, 但父级没有定位, 以浏览器窗口为参照为进行定位
*/
position: absolute;
/* left: 50px; */
left: 0;
top: 0;
/*
1. 脱标, 不占位
2. 改变标签的显示模式特点: 具体行内块特点(在一行共存, 宽高生效)
*/
width: 200px;
height: 200px;
background-color: pink;
}
</style>
</head>
<body>
<p>测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位</p>
<p>测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位</p>
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<p>测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位</p>
<p>测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位</p>
<div class="box">box</div>
<p>测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位</p>
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</body>
</html>6.1 Paternity
➢ Scene: Let the child element move freely relative to the parent element
➢ Meaning:
• Child elements: absolutely positioned
• Parent element: relative positioning
➢ The benefits of son and father: The parent element is positioned relatively, and has the least impact on the layout of the web page
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
.father {
position: relative;
width: 400px;
height: 400px;
background-color: pink;
}
.son {
/* 相对, 绝对 */
/* 父级相对定位; 子级绝对定位 -- 子绝父相 */
/* position: relative; */
/* position: absolute; */
/* right: 100px; */
width: 300px;
height: 300px;
background-color: skyblue;
}
.sun {
position: absolute;
/* left: 20px;
top: 30px; */
right: 20px;
bottom: 50px;
width: 200px;
height: 200px;
background-color: green;
}
/* 绝对定位查找父级的方式: 就近找定位的父级, 如果逐层查找不到这样的父级, 就以浏览器窗口为参照进行定位 */
</style>
</head>
<body>
<div class="father">
<div class="son">
<div class="sun"></div>
</div>
</div>
</body>
</html>Case: The case of the son and father being in the middle
Idea 1: Use absolute positioning, left: 50%, and margin-left: - (half the width of the child element)
Idea 2: Use absolute positioning, left: 50%, and then use displacement: half of its own width and height , transform: translate(-50%, -50%);
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
.box {
/* 1. 绝对定位的盒子不能使用左右margin auto居中 */
position: absolute;
/* margin: 0 auto; */
/* left: 50%, 整个盒子移动到浏览器中间偏右的位置 */
left: 50%;
/* 把盒子向左侧移动: 自己宽度的一半 */
/* margin-left: -150px; */
top: 50%;
/* margin-top: -150px; */
/* 位移: 自己宽度高度的一半 */
transform: translate(-50%, -50%);
width: 400px;
height: 300px;
background-color: pink;
}
</style>
</head>
<body>
<div class="box"></div>
</body>
</html>Case 2: Navigation QR code centering case
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
* {
margin: 0;
padding: 0;
}
/* 因为有通栏：占满一行的边框，所以需要有一个通栏：占满一行的盒子 */
.nav {
height: 40px;
border-bottom: 1px solid #ccc;
}
/* 因为ul中所有的内容都是在网页的宽度固定并且水平居中的盒子内部，所以设置ul为宽度固定并且水平居中的效果（后面项目中所用到的版心） */
ul {
list-style: none;
width: 1200px;
margin: 0 auto;
}
ul li {
float: left;
width: 20%;
height: 40px;
border-right: 1px solid #ccc;
/* 自动内减 */
box-sizing: border-box;
text-align: center;
line-height: 40px;
}
ul .last {
border-right: none;
}
ul li a {
/* a标签默认是行内元素，宽高由内容撑开，并且无法设置宽高，此时默认情况用户只能点击文字区域才能调整 */
/* 如果把a标签转换成块级元素，此时可以设置宽高，会让a标签范围更大，用户可以点击调整的区域也越大 */
display: block;
/* 宽度不设置块元素会默认占满一行 */
height: 40px;
text-decoration: none;
color: #000;
}
ul li .app {
position: relative;
}
.code {
position: absolute;
left: 50%;
top: 41px;
transform: translate(-50%);
}
</style>
</head>
<body>
<!-- 导航 -->
<div class="nav">
<ul>
<li><a href="#">我要投资</a></li>
<li><a href="#">平台介绍</a></li>
<li><a href="#">新手专区</a></li>
<!-- 因为用户鼠标放在二维码图片上也能跳转，所以证明img也是在a的范围内，因此把img写在a标签的内部 -->
<li><a href="#" class="app">手机微金所 <img src="./images/code.jpg" alt="" class="code"> </a></li>
<li class="last"><a href="#">个人中心</a></li>
</ul>
</div>
</body>
</html>(Case) The case where the father and son are centered horizontally and vertically - solution
1. Parenthood
2. Let the sub-box go to the right half of the big box • left: 50%
3. Let the child box go down half of the big box • top: 50%
4. Let the child box go left + go up half of its own • transform: translate(-50%, -50%);
7. Fixed positioning
➢ Introduction: Obsessive positioning, positioning and moving relative to the browser
➢ Code:
position:fixed➢ Features:
1. It needs to cooperate with the orientation attribute to realize the movement
2. Move relative to the viewable area of the browser
3. Does not occupy a position on the page → has been unmarked
➢ Application scenario: Let the box be fixed at a certain position on the screen
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
/* css书写: 1. 定位 / 浮动 / display ; 2. 盒子模型; 3. 文字属性 */
.box {
position: fixed;
left: 0;
top: 0;
/*
1. 脱标-不占位置
2. 改变位置参考浏览器窗口
3. 具备行内块特点
*/
width: 200px;
height: 200px;
background-color: pink;
}
</style>
</head>
<body>
<p>测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位测试定位</p>
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<div class="box">box</div>
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</body>
</html>8.1 Positioning Hierarchy
➢ Hierarchical relationship of elements in different layout modes:
• standard stream<float<positioned
➢ Hierarchical relationship between different positioning:
• The relative, absolute, and fixed default levels are the same • At this time, the elements written below in HTML have a higher level and will cover the elements above
8.2 Changing the hierarchy of positioned elements
➢ Scene: Change the hierarchy of positioned elements
➢ Attribute name: z-index
➢ Attribute value: number • The larger the number, the higher the level
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
div{
width: 200px;
height: 200px;
}
.one{
position: absolute;
left: 20px;
top: 50px;
background-color: pink;
/* z-index: 1; */
}
.two{
position: absolute;
left: 50px;
top: 100px;
background-color: skyblue;
}
</style>
</head>
<body>
<!-- 有定位的盒子，默认情况下，层级关系有一个原则：后来者居上 -->
<!--
z-index属性：改变标签层级，数字越大，显示层级越高，z-index的默认值是0
z-index必须配合定位才能生效
-->
<div class="one">one</div>
<div class="two">two</div>
</body>
</html>9. Summary
2. Decoration
1.1 Knowing the Baseline
➢ Baseline: There is a baseline (baseline) for alignment in the typesetting of text type elements in browsers
1.2 Text alignment problem
➢ Scenario: Solve the problem of vertical alignment of inline/inline block elements
➢ Problem: When the picture and text are displayed in one line, the bottom is not aligned
1.3 Vertical alignment
➢ Property name: vertical-align
➢ Attribute value:
| attribute value | Effect |
| baseline | Default, baseline alignment |
| top | align top |
| middle | center alignment |
| bottom | align top |
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
/* 浏览器遇到行内和行内块标签当做文字处理, 默认文字是按基线对象 */
input {
height: 50px;
box-sizing: border-box;
vertical-align: middle;
}
</style>
</head>
<body>
<div>
<input type="text"><input type="button" value="搜索">
</div>
</body>
</html>(Expansion) Problems that can be solved by vertical-align in the project
1. The text box and form button cannot be aligned
2. Input and img cannot be aligned
3. The text box in the div, the text box cannot be pasted to the top
4. The div does not set a height and is stretched by the img tag. At this time, there will be an additional gap problem under the img tag
5. Use line-height to center the img tag vertically
2.1 Cursor Type
➢ Scene: set the style displayed when the mouse cursor is on the element
➢ Attribute name: cursor
➢ Common attribute values:
| attribute value | Effect |
| default | Default value, default is arrow |
| pointer | Small hand effect, reminding users that they can click |
| text | I font, prompting the user to select text |
| move | Cross cursor, prompting user to move |
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
div {
width: 200px;
height: 200px;
background-color: pink;
/* 手型 */
/* cursor: pointer; */
/* 工字型, 表示可以复制 */
/* cursor: text; */
/* 十字型, 表示可以移动 */
cursor: move;
}
</style>
</head>
<body>
<div>div</div>
</body>
</html>3.1 Border rounded corners
➢ Scene: round the four corners of the box, increase page details, and improve user experience
➢ Attribute name: border-radius
➢ Common values: number+px, percentage
➢ Principle:
Assignment rules: start assigning values from the upper left corner, then assign values clockwise, and look at the opposite corner if there is no assignment! clockwise.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
.box {
margin: 50px auto;
width: 200px;
height: 200px;
background-color: pink;
/* 一个值: 表示4个角是相同的 */
border-radius: 10px;
/* 4值: 左上 右上 右下 左下 -- 从左上顺时针转一圈 */
/* border-radius: 10px 20px 40px 80px; */
/* border-radius: 10px 40px 80px; */
/* border-radius: 10px 80px; */
}
</style>
</head>
<body>
<div class="box"></div>
</body>
</html>3.2 Common applications of frame rounded corners
➢ To draw a perfect circle:
1. The box must be square
2. Set the border fillet to be half the width and height of the box → border-radius:50%
➢ Capsule button:
1. The box is required to be rectangular
2. Settings → border-radius: Half the height of the box
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
.one {
width: 200px;
height: 200px;
background-color: pink;
/* border-radius: 100px; */
/* 50% : 取盒子尺寸的一半 */
border-radius: 50%;
}
/* 胶囊状: 长方形, border-radius取值是高度的一半 */
.two {
width: 400px;
height: 200px;
background-color: skyblue;
border-radius: 100px;
}
</style>
</head>
<body>
<div class="one"></div>
<div class="two"></div>
</body>
</html>4.1 The display effect of the overflow part
➢ Overflow part: refers to the area where the content of the box exceeds the scope of the box
➢ Scene: control the display effect of the overflowing part of the content, such as: display, hide, scroll bar...
➢ Property name: overflow
➢ Common attribute values:
| attribute value | Effect |
| visible | The default value, the default is overflow visible |
| hidden | overflow hidden |
| scroll | Show scrollbars regardless of overflow |
| act | Automatically show or hide scrollbars based on overflow |
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
.box {
width: 300px;
height: 300px;
background-color: pink;
/* 溢出隐藏 */
overflow: hidden;
/* 滚动: 无论内容是否超出都显示滚动条的位置 */
/* overflow: scroll; */
/* auto: 根据内容是否超出, 判断是否显示滚动条 */
/* overflow: auto; */
}
</style>
</head>
<body>
<div class="box">我是div,测试溢出显示效果我是div</div>
</body>
</html>5.1 The element itself is hidden
➢ Scene: Make an element itself invisible on the screen. Such as: mouse: element hidden after hover
➢ Common attributes:
1. visibility：hidden
2. display：none
➢ Difference:
1. visibility: hidden hides the element itself and occupies a position in the web page
2. display: none hides the element itself and does not occupy a position in the web page
➢ Notes:
• In development, the display and hide switching of elements is often completed through the display attribute
• display: none; (hide), display: block; (display)
5.2 Element display hide switch case
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
div {
width: 200px;
height: 200px;
}
.one {
/* 占位隐藏 */
/* visibility: hidden; */
/* **** 不占位隐藏 */
display: none;
background-color: pink;
}
.two {
background-color: green;
}
</style>
</head>
<body>
<div class="one">one</div>
<div class="two">two</div>
</body>
</html>6. Expand
(Extended) The overall transparency of the element
➢ Scene: Make an element as a whole (including content) transparent
➢ Property name: opacity
➢ Attribute value: a number between 0 and 1 • 1: means completely opaque • 0: means completely transparent
➢ Points to note: • opacity will make the element transparent as a whole, including the content inside, such as: text, sub-elements, etc...
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
div {
width: 400px;
height: 400px;
background-color: green;
opacity: 0.5;
}
</style>
</head>
<body>
<div>
<img src="./images/product.png" alt="">
这个字透明吗
</div>
</body>
</html>(Extended) border merging
➢ Scenario: Merge the borders of adjacent tables to get the effect of a thin line border ➢ Code: border-collapse: collapse;
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
table {
border: 1px solid #000;
/* 注意: 一定要加给table标签 : 做细线表格 */
border-collapse: collapse;
}
th,
td {
border: 1px solid #000;
}
</style>
</head>
<body>
<!-- border="1" width="400" height="300"cellspacing="0" -->
<table>
<caption><h3>前端与移动开发学员学习情况</h3></caption>
<thead>
<tr>
<th>编号</th>
<th>姓名</th>
<th>性别</th>
<th>成绩</th>
</tr>
</thead>
<tbody>
<tr>
<td>1</td>
<td>小姐姐</td>
<td>女</td>
<td>100</td>
</tr>
<tr>
<td>2</td>
<td>小哥哥</td>
<td>男</td>
<td>100</td>
</tr>
<tr>
<td>3</td>
<td>大姐姐</td>
<td>女</td>
<td>100</td>
</tr>
</tbody>
<tfoot>
<tr>
<td colspan="2">总成绩</td>
<td colspan="2">300</td>
</tr>
</tfoot>
</table>
</body>
</html>(Expansion) Skills of drawing triangles with CSS (interview questions)
➢ 场景：在网页中展示出小三角形时，除了可以使用图片外，还可以使用代码完成。
➢ 实现原理：
• 利用盒子边框完成
➢ 实现步骤：
1. 设置一个盒子
2. 设置四周不同颜色的边框
3. 将盒子宽高设置为0，仅保留边框
4. 得到四个三角形，选择其中一个后，其他三角形（边框）设置颜色为透明
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
div {
/* width: 100px;
height: 100px; */
width: 0;
height: 0;
/* background-color: pink; */
/* transparent: 透明 */
border-top: 100px solid transparent;
border-right: 100px solid transparent;
border-bottom: 100px solid transparent;
border-left: 100px solid orange;
}
/*
1. 书写一个盒子
2. 盒子添加四个方向的border, 颜色设置不同
3. 保留其中一个方向的border, 其他方向颜色是transparent
*/
</style>
</head>
<body>
<div></div>
</body>
</html>