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Learning about inline elements and block-level elements_html/css_WEB-ITnose
- WBOYOriginal
- 2016-06-24 11:39:221859browse
Learning about inline elements and block-level elements
@(css)[Miaotong]
css standard document flow:
Abbreviated as "standard flow", it refers to the arrangement rules of various elements when other special CSS rules related to arrangement and positioning are not used. Elements in HTML documents can be divided into block-level elements and inline elements.
Block-level elements: always expressed in the form of a block, and arranged vertically with brothers at the same level, filling the left and right sides.
Inline elements: Inline elements do not occupy a separate space and are attached to block-level elements. Inline elements do not have their own area. It is also a node in the DOM tree. At this point, there is no difference between inline elements and block-level elements. The width and height of inline elements cannot be set, but they can be located on the same line as other inline elements. Inline elements generally cannot contain block-level elements. The height of an inline element is generally determined by the font size inside the element, and the width is controlled by the length of the content. Common inline elements include a, em, strong, etc.
Principles of positioning boxes in the standard flow (See my last article: Talk about the box model)
(1) Level between inline elements margin
When two inline elements are adjacent to each other, the distance between them is the margin-right of the first element plus the margin-left of the second element.
(2) Vertical margin between block-level elements
When two block-level elements are immediately adjacent, their distance is not the sum of margin-bottom and margin-top, but the larger of the two. .
(3) Margin between nested boxes
When a div block is contained within another div block, a typical parent-child relationship is formed. The margin of the child block will be based on the content of the parent block.
(4) Set margin to a negative value
When margin is set to a negative value, the block set to a negative number will move in the opposite direction, or even cover other blocks.
The code demonstration is as follows:
<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>CSS</title> <style> ul{ border:1px solid red; } li{ border:1px solid green; } strong{ border:1px solid #000; } </style></head><body> <ul> <li>第1个列表的第1个项目内容</li> <li>第1个列表的第2个<strong>项目内容</strong>,内容更长一些， 目的是演示自动折行的效果。</li> </ul> <ul> <li>第2个列表的第1个项目内容</li> <li>第2个列表的第2个项目内容，内容更长一些，目的是演示自动折行 的效果。</li> </ul> </body></html> Page effect:
如上代码所示，其内容是body中有两个列表（ul），ul列表中又各有两个列表项目（li）。一共有四层，顶层为body，第二层为ul，第三层为li，第四层为文本。ul和li都为块级元素，而strong则为行内元素，从 DOM 的角度来看，块级元素和行内元素是没有区别的，都是树上的一个节点，而从 CSS 的角度来看，二者就有很多的区别，块级元素有属于自己的区域，而行内元素没有！就如页面效果图所示。标准流就是 CSS 规定的默认的块级无素和行内元素的排列方式。从body标记开始，依次把其中的子元素放到适当的位置。如果一个html更为复杂，层次更多，那么也和这个一样，直至所有的元素被检查一遍，分配到相应的区域。在这个过程，一个一个的盒子自然地形成一个序列，同级别的盒子依次排列在父级盒子中，就像一条河流有干流和支流一样，这就是被称为“流”的原因。
Characteristics of inline elements:
Characteristics of block-level elements:
If I set the line-height of strong, the effect is as follows:
strong{ border:1px solid #000; line-height:50px; } Page effect:
As shown above, the setting of line-height changes the height of the inline element strong.
If we set the height of strong, the effect is as follows:
strong{ border:1px solid #000; height:50px; } Page effect:
As shown above, the setting of height, inline elements The height of strong has not changed.
Code:
li{ border:1px solid green; margin-left:20px; margin-right:20px; margin-top:20px; margin-bottom:20px; } strong{ border:1px solid #000; margin-left:20px; margin-right:20px; margin-top:20px; margin-bottom:20px; } Page rendering:
As shown above, for the inline element strong, margin-left and margin -right is valid, but margin-top and margin-bottom are invalid. For the block-level element li, the upper, lower, left and right margins are all valid.
Code:
li{ border:1px solid green; padding-left:20px; padding-right:20px; padding-top:20px; padding-bottom:20px; } strong{ border:1px solid #000; padding-left:20px; padding-right:20px; padding-top:30px; padding-bottom:20px; } Page image:
As shown above, for the inline element strong, padding-left and padding-right are valid, However, padding-top and padding-bottom are invalid. Only the upper and lower ranges are expanded, but the content of other elements is not changed. For the block-level element li, the top, bottom, left and right padding is valid.
The difference between inline elements and block-level elements:
Inline elements will be arranged in a straight line, all on the same line, arranged horizontally,
Block-level elements each occupy one line and are arranged vertically. Block-level elements start on a new line and end with a line break.
Block-level elements can contain inline elements and block-level elements. Inline elements cannot contain block-level elements.
The difference in attributes between inline elements and block-level elements is mainly due to the box model attributes
The text-align attribute is the difference between the two expressions
In Section 16.2 of the W3C CSS2.1 specification, text-align align is described in detail:
值： left | right | center | justify | inherit
Initial value: anonymous value, determined by the value of 'direction', if 'direction' is 'ltr' then it is 'left', if 'direction' ' is 'rtl', then 'right'.
Applies to: block-level elements, table cells, inline block elements
Inheritance: Yes
计算后的值：初始值或指定值
这个特性描述了如何使一个块元素的行内内容对齐。
注意一点，标准里说这个属性是用来对齐行内内容的，所以，不应该对块级内容起作用。
解释一下，行内内容是说由行内元素组成的内容，比如 SPAN 元素，IFRAME元素和元素样式的 ‘display : inline’ 的都是行内元素；块级内容跟则是由块级元素构成，DIV 是最常用的块级元素。块级元素和行内元素的区别是，块级元素会占一行显示，而行内元素可以在一行并排显示。
这样，我们对这个特性的认识应该就清楚了。但是，虽然标准里这么规定，那么是不是所有浏览器都遵守呢？答案是否定的。
IE6/7及IE8混杂模式中，text- align:center可以使块级元素也居中对齐。其他浏览器中，text-align:center仅作用于行内内容上。
解决上面的问题比较好的方式，就是为所有需要相对父容器居中对齐的块级元素设置“margin-left:auto; margin-right:auto”。但这个方式 IE6/IE7/IE8的混杂模式中不支持，所以还要设置父容器的 "text-align:center;"。若居中对齐的子元素内的行内内容不需要居中对齐，则还需要为其设置“text-align:left”。
代码：
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>CSS</title> <style> body{ width:800px; border:1px solid #000; } div.wrapper{ /*margin:0 auto;*/ width:500px; border:1px solid red; text-align: center; } div.box1{ border:1px solid red; } div strong{ border:1px solid green; } </style> </head> <body> <div class="wrapper"> <div class="box1"> <strong>我是行内元素</strong> </div> <p>我是块级元素</p> </div> </body> </html> 页面：
IE8/Firefox/Chrome/Safari/Opera:
IE6/IE7:
代码：
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>CSS</title> <style> body{ width:800px; border:1px solid #000; } div.wrapper{ margin:0 auto; width:500px; border:1px solid red; } div.box1{ border:1px solid red; text-align:center; } div strong{ border:1px solid green; } </style> </head> <body> <div class="wrapper"> <div class="box1"> <strong>我是行内元素</strong> </div> <p>我是块级元素</p> </div> </body> </html> IE8/Firefox/Chrome/Safari/Opera:
IE6/IE7：
代码：
<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>CSS</title> <style> body{ width:800px; border:1px solid #000; } div.wrapper{ margin:0 auto; width:500px; border:1px solid red; text-align:center; } div.box1{ border:1px solid red; } div strong{ border:1px solid green; } </style></head><body> <div class="wrapper"> <div class="box1"> <strong>我是行内元素</strong> </div> <p>我是块级元素</p> </div></body></html> IE6/IE7/IE8/Firefox/Chrome/Safari/Opera:
块级元素、行内元素分别汇总如下：
Examples of block level elements
block level elements|Element Description<address> information on author<blockquote> long quotation<button> push button<caption> table caption<dd> definition description<del> deleted text<div> generic language/style container<dl> definition list<dt> definition term<fieldset> form control group<form> interactive form<h1> heading<h2> heading<h3> heading<h4> heading<h5> heading<h6> heading<hr> horizontal rule<iframe> inline subwindow<ins> inserted text<legend> fieldset legend<li> list item<map> client-side image map<noframes> alternate content container for non frame-based rendering<noscript> alternate content container for non script-based rendering<object> generic embedded object<ol> ordered list<p> paragraph<pre class="brush:php;toolbar:false"> preformatted text<table> table<tbody> table body<td> table data cell<tfoot> table footer<th> table header cell<thead> table header<tr> table row<ul> unordered list
Examples of inline elements
inline elements | Element Description<a> anchor<abbr> abbreviated form<acronym> acronym<b> bold text style<bdo> I18N BiDi over-ride<big> large text style<br> forced line break<button> push button<cite> citation<code> computer code fragment<del> deleted text<dfn> instance definition<em> emphasis<i> italic text style<iframe> inline subwindow<img> Embedded image<input> form control<ins> inserted text<kbd> text to be entered by the user<label> form field label text<map> client-side image map<object> generic embedded object<q> short inline quotation<samp> sample program output, scripts, etc.<select> option selector<small> small text style<span> generic language/style container<strong> strong emphasis<sub> subscript<sup> superscript<textarea> multi-line text field<tt> teletype or monospaced text style<var> instance of a variable or program argument
块级元素列表
<address> 定义地址<caption> 定义表格标题<dd> 定义列表中定义条目<div> 定义文档中的分区或节<dl> 定义列表<dt> 定义列表中的项目<fieldset> 定义一个框架集<form> 创建 HTML 表单<h1> 定义最大的标题<h2> 定义副标题<h3> 定义标题<h4> 定义标题<h5> 定义标题<h6> 定义最小的标题<hr> 创建一条水平线<legend> 元素为 fieldset 元素定义标题<li> 标签定义列表项目<noframes> 为那些不支持框架的浏览器显示文本，于 frameset 元素内部<noscript> 定义在脚本未被执行时的替代内容<ol> 定义有序列表<ul> 定义无序列表<p> 标签定义段落<pre class="brush:php;toolbar:false"> 定义预格式化的文本<table> 标签定义 HTML 表格<tbody> 标签表格主体（正文）<td> 表格中的标准单元格<tfoot> 定义表格的页脚（脚注或表注）<th> 定义表头单元格<thead> 标签定义表格的表头<tr> 定义表格中的行
行内元素列表
<a> 标签可定义锚<abbr> 表示一个缩写形式<acronym>定义只取首字母缩写<b> 字体加粗<bdo> 可覆盖默认的文本方向<big> 大号字体加粗<br> 换行<cite> 引用进行定义<code> 定义计算机代码文本<dfn> 定义一个定义项目<em> 定义为强调的内容<i> 斜体文本效果<img> 向网页中嵌入一幅图像<input> 输入框<kbd> 定义键盘文本<label> 标签为 input 元素定义标注（标记）<q> 定义短的引用<samp> 定义样本文本<select>创建单选或多选菜单<small> 呈现小号字体效果<span> 组合文档中的行内元素<strong>语气更强的强调的内容<sub> 定义下标文本<sup> 定义上标文本<textarea>多行的文本输入控件<tt> 打字机或者等宽的文本效果<var> 定义变量
可变元素素列表--可变元素为根据上下文语境决定该元素为块级元素或者内联元素
<button> 按钮<del> 定义文档中已被删除的文本<iframe> 创建包含另外一个文档的内联框架（即行内框架）<ins> 标签定义已经被插入文档中的文本<map> 客户端图像映射（即热区）<object> object对象<script> 客户端脚本
行内元素转换为块级元素
display:block; (字面意思表现形式设为块级) display:inline; display:inline-block;
可以通过修改样式display属性改变元素是以块级还是行内元素呈现，当display的值设为block时，元素将以块级方式呈现；当display值设为inline时，元素将以行内形式呈现。
如果想让一个元素可以设置宽度高度，又让它以行内形式显示，我们可以设置display的值为inline-block。
假如有不足或者错误的地方，欢迎指正哟。-------妙瞳