This article mainly introduces the analysis of the positon attribute of CSS. It has a certain reference value. Now I share it with you. Friends in need can refer to it.
Position is a very important attribute in CSS. , through the position attribute, we can offset the element relative to its normal position, parent element or browser window. Position is also an attribute that beginners can easily get confused about. This article will start with the most basic knowledge and talk about some theories and applications about the position attribute.
Basic knowledge
The postion attribute is called positioning. It has 4 different types of positioning. These types will affect the way elements are generated. Below we explain the position attribute in detail. .
Four types of position
(1)static
static is the default value of the position attribute. By default, block-level elements and inline elements are displayed according to their respective characteristics
(2) relative
relative is translated into Chinese as relative positioning. After setting this attribute, the element will be offset according to top, left, bottom, and right. The key point is that its original space is still retained. Let’s look at the following example:
HTML code
1 <p> 2 </p> 3 <p></p>
CSS code
1 p { background: #0094ff; width: 250px; height: 100px; } 2 .relative { background: #ff6a00; position: relative; width: 200px; height: 100px; top: 20px; left: 50px; }
Rendering
After the element is set to absolute, it will be separated from the document flow and will not occupy the original space. Subsequent elements will replace it, and whether the element is an inline element or a block-level element, it will be generated A block-level box, that is, for example, the inline element span can set the height and width attributes after setting absolute. Look at the following example:
HTML code
1 <span class="absolute"> 2 </span> 3 <p></p>CSS code
1 p { background: #0094ff; width: 250px; height: 100px; } 2 .absolute { background: #ff6a00; position: absolute; width: 200px; height: 100px; top: 20px; left: 50px; }Rendering
##absolute effect
As shown in the figure, if the span tag is set to absolute positioning, the height and width attributes can be set without occupying the original space. The subsequent p element will replace it.
(4) fixed
The performance of fixed is similar to absolute, but compared with absolute's offset relative to an uncertain parent element, fixed is offset relative to the browser window
Containing block
In
Detailed explanation of CSS float attribute we mentioned the concept of containing block. There is also a containing block attribute for the position attribute, which will be discussed in several cases: 1. The containing block of the root element. The root element is usually an html element. Some browsers will use body as the root element. Most browsers will use body as the root element. , the initial containing block is a rectangle of the size of the viewport 2. The containing block of the non-root element, if the position of the element is relative or static, its containing block is the nearest block-level box, table cell or inline block The content boundary
Let’s take an example to illustrate,
HTML code
1 <p> 2 我是父级元素的内容 3 <p class="relative"> 4 相对定位元素 5 </p> 6 </p>
CSS code
p { background: #0094ff; width: 250px; height: 100px; } .relative { background: #ff6a00; position: relative; width: 200px; height: 100px; top: 20px; left: 50px; }
Rendering
contains Block
This is the containing block of the relatively positioned element, which is the content boundary of the nearest block-level box, table cell or inline block. The relatively positioned element is offset relative to its containing block. We can simply understand To offset relative to its original position.
3. The containing block of a non-root element. If the position of the element is absolute, the containing block is the nearest ancestor element whose position is not static.
Simply put, its containing block will search upwards from the parent element until it finds the first element whose position is not static.
Offset attribute
The previous example has already involved the offset attribute, which refers to the offset of the element relative to its containing block. We call it the offset attribute, respectively. top, bottom, left, right, respectively represent up, down, left and right. Their values can be specific numerical values or percentages. If it is a percentage, top and bottom are percentages relative to the height of the containing block, and left and right are percentages relative to the width. They can also be set to negative values, potentially moving the element outside the containing block.
Absolute positioning
Next let’s take a look at the details of absolute positioning.
Basic absolute positioning
When an element is set to absolute positioning, it will be separated from the document flow and then offset relative to its containing block.
Generally speaking, we will set an element to relative as the containing block of the absolute element. Let's look at the following example:HTML code
1 <p class="absolute"> 2 相对于初始Analysis of CSS positon attribute定位 3 </p> 4 <br /> 5 <br /> 6 <br /> 7 <br /> 8 <br /> 9 <br /> 10 <p class="relative"> 11 <p class="absolute"> 12 相对于最近relative祖先元素定位 13 </p> 14 </p>
CSS code
1 p { background: #0094ff; width: 250px; height: 100px; } 2 .relative { background: #ff6a00; position: relative; width: 200px; height: 100px; top: 20px; left: 50px; } 3 .absolute { background: #988c8c; position: absolute; width: 200px; height: 100px; top: 20px; left: 50px; }
effect图
Analysis of CSS positon attribute
如图所示,有两个绝对定位元素,第一个元素没有position不是static的祖先元素,所以它的Analysis of CSS positon attribute是body,根据body进行偏移,
第二个绝对定位元素设置了一个relative的父元素,它根据父元素进行偏移。
Analysis of CSS positon attribute
元素设置成绝对定位后会脱离文档流,并且失去占用的空间,而且如果偏移的位置接近,会造成重叠问题。看看下面的例子:
HTML代码
1 <p class="relative"> 2 <p class="absolute"> 3 相对于最近relative祖先元素定位1 4 </p> 5 <p class="absolute light"> 6 相对于最近relative祖先元素定位2 7 </p> 8 </p>
CSS代码
1 p { background: #0094ff; width: 250px; height: 100px; } 2 .relative { background: #ff6a00; position: relative; width: 500px; height: 300px; top: 20px; left: 50px; } 3 .absolute { background: #988c8c; position: absolute; width: 200px; height: 100px; top: 20px; left: 50px; } 4 .light { background: #f3d6d6; top: 70px; left: 80px; }
效果图
Analysis of CSS positon attribute
我们可以看到,第二个绝对定位元素盖住了第一个元素,那怎么让第一个元素盖住第二个元素呢,这就要用到z-index属性,这个属性表示元素的叠加顺序,默认情况下,z-index为0,数值越高的元素层级越高,就可以盖住低于其层级的元素,我们设置第一个原色的z-index为10,结果如下
Analysis of CSS positon attribute
如果两个元素的层级相同,则越后面的元素会覆盖前面的元素,默认情况下,第二个元素就会盖住第一个元素。
固定定位
fixed定位很简单,类似与absoulte,但是它的Analysis of CSS positon attribute就是浏览器窗口,相对来说简单很多。常见的应用比如固定导航,回到顶部。在这里不再赘述,大家可以查找相关资料。
相对定位
relative定位的元素进行偏移后,不会脱离文档流,还有占据原本的空间。除此之外,我们还要注意一个细节:如果元素设置了margin为负值之后发生重叠的情况下,相对定位的元素会覆盖普通元素。我们看看下面的例子:
HTML代码
1 <p class="no-relative"> 2 未相对定位的元素 3 </p> 4 <p class="minus-margin"> 5 负margin元素 6 </p>
CSS代码
1 p { background: #0094ff; width: 250px; height: 100px; } 2 .no-relative { background: #ff6a00; width: 200px; height: 100px; } 3 .relative { background: #ff6a00; width: 200px; height: 100px; position: relative; } 4 .minus-margin { margin-top: -30px; }
效果图
Analysis of CSS positon attribute
默认情况下,两个元素都是正常的元素,设置了负的margin属性后,后面的元素会覆盖前面的元素,我们修改第一个元素的class为relative,可以看到效果如下:
Analysis of CSS positon attribute
添加了相对定位后,第一个元素就会覆盖其他正常的元素了。
relative属性最经常的一个应用应该是作为absolute元素的Analysis of CSS positon attribute了,为了限制absolute元素的偏移位置,常常设置其父元素为relative来作为其Analysis of CSS positon attribute。
应用举例
position的应用非常频繁,下面我来说说常见的一些场景:
Analysis of CSS positon attribute
在电商网站中,我们常常可以看到产品的左上角或右上角有一些比如“新品”,“促销”,“热卖”等标签,比如下图:
Analysis of CSS positon attribute
这个是怎么实现的呢,我们来模拟一下:
HTML代码:
1 <p class="product"> 2 我是产品 3 <span class="hot"> 4 热卖 5 </span> 6 </p>
CSS代码:
1 .product { width: 150px; height: 150px; background: #0094ff; position: relative; } 2 .hot { position: absolute; right: 10px; top: 10px; width: 40px; height: 20px; background: #ff6a00; text-align: center; }
效果如下:
Analysis of CSS positon attribute
如图所示,右上角有一个标签。原理很简单,就是设置父元素相对定位,标签元素绝对定位,然后相对于父元素偏移到右上角。
自动完成框
自动完成框是一个非常常见的应用,其生成的下拉菜单也是用到了position属性。我们先看看下面的效果:
Analysis of CSS positon attribute
这是一个很简单常见的下来自动完成框,我们来看看它的HTML和CSS代码:
HTML代码
1 <input class="search-box" type="text" placeholder="请输入关键字" value="position" /> 2 <ul style="left:58px;"> 3 <li>position属性</li> 4 <li>position应用</li> 5 <li>position是什么</li> 6 <li>position翻译</li> 7 </ul>
CSS代码
1 .search-box { border: 1px solid #ccc; width: 200px; padding: 5px; height: 24px; margin-left: 50px; } 2 ul, li { list-style-type: none; } 3 ul { border: 1px solid #ccc; width: 210px; position: absolute; } 4 li { padding: 5px; }
这个原理也很简单,通过设置下拉菜单为绝对定位,然后设置其left属性与输入框对齐。
Of course, there are many applications of position, such as layout. For example, fixed can be used to make fixed navigation menus, fixed menus in the lower right corner of web pages, etc. Interested students can find relevant information for learning.
Summary
The position attribute is an attribute that can easily confuse beginners, especially the applications of absolute and relative. To make good use of them, you must first understand the basic characteristics of absolute and relative. After understanding their characteristics, they will be easy to apply. After understanding the basic principles, write a few examples to experience their characteristics in practice, and slowly You will become familiar with it.
The above is the entire content of this article. I hope it will be helpful to everyone's study. For more related content, please pay attention to the PHP Chinese website!
Related recommendations:
##How to set placeholder through css
About css control UL
LI style analysis
The above is the detailed content of Analysis of CSS positon attribute. For more information, please follow other related articles on the PHP Chinese website!

在css中,可用list-style-type属性来去掉ul的圆点标记,语法为“ul{list-style-type:none}”;list-style-type属性可设置列表项标记的类型,当值为“none”可不定义标记,也可去除已有标记。

区别是:css是层叠样式表单,是将样式信息与网页内容分离的一种标记语言,主要用来设计网页的样式,还可以对网页各元素进行格式化;xml是可扩展标记语言,是一种数据存储语言,用于使用简单的标记描述数据,将文档分成许多部件并对这些部件加以标识。

在css中,可以利用cursor属性实现鼠标隐藏效果,该属性用于定义鼠标指针放在一个元素边界范围内时所用的光标形状,当属性值设置为none时,就可以实现鼠标隐藏效果,语法为“元素{cursor:none}”。

在css中,rtl是“right-to-left”的缩写,是从右往左的意思,指的是内联内容从右往左依次排布,是direction属性的一个属性值;该属性规定了文本的方向和书写方向,语法为“元素{direction:rtl}”。

转换方法:1、给英文元素添加“text-transform: uppercase;”样式,可将所有的英文字母都变成大写;2、给英文元素添加“text-transform:capitalize;”样式,可将英文文本中每个单词的首字母变为大写。

在css中,可以利用“font-style”属性设置i元素不是斜体样式,该属性用于指定文本的字体样式,当属性值设置为“normal”时,会显示元素的标准字体样式,语法为“i元素{font-style:normal}”。

在css3中,可以用“transform-origin”属性设置rotate的旋转中心点,该属性可更改转换元素的位置,第一个参数设置x轴的旋转位置,第二个参数设置y轴旋转位置,语法为“transform-origin:x轴位置 y轴位置”。


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

SAP NetWeaver Server Adapter for Eclipse
Integrate Eclipse with SAP NetWeaver application server.

EditPlus Chinese cracked version
Small size, syntax highlighting, does not support code prompt function

Dreamweaver Mac version
Visual web development tools

Notepad++7.3.1
Easy-to-use and free code editor

VSCode Windows 64-bit Download
A free and powerful IDE editor launched by Microsoft
