Please let me know why the padding-bottom and padding-right are extra when setting the same padding for the li element_html/css

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Please let me know why the padding-bottom and padding-right are extra when setting the same padding for the li element_html/css_WEB-ITnose

Jun 24, 2016 am 11:40 AM

The code is as follows

&lt;!DOCTYPE html PUBLIC &quot;-//W3C//DTD XHTML 1.0 Transitional//EN&quot; &quot;http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd&quot;&gt;&lt;html xmlns=&quot;http://www.w3.org/1999/xhtml&quot;&gt;&lt;head&gt;&lt;meta http-equiv=&quot;Content-Type&quot; content=&quot;text/html; charset=gb2312&quot; /&gt;&lt;title&gt;无标题文档&lt;/title&gt;&lt;style&gt;	body,div,dl,dt,dd,ul,ol,li,h1,h2,h3,h4,h5,h6,pre,form,fieldset,input,textarea,p,blockquote,th,td,img {padding:0;margin:0;} 	#div1{		margin:10px;		width:300px;		height:200px;	}	#div1 textarea{		width:300px;		height:180px;	}	#div2{		margin:10px auto;		height:400px;		width:400px;		border:1px solid black;		overflow:auto;	}	#div2 ul li{		border-bottom:1px dashed black;		list-style:none;		padding:10px 10px 10px 10px;			}&lt;/style&gt;&lt;script type=&quot;text/javascript&quot;&gt;	window.onload=function(){		var adiv1=document.getElementById(&quot;div1&quot;);		var adiv2=document.getElementById(&quot;div2&quot;);		var obtn=adiv1.getElementsByTagName(&quot;input&quot;)[0];		var otxt=adiv1.getElementsByTagName(&quot;textarea&quot;)[0];		var oul=document.getElementById(&quot;ul1&quot;);		obtn.onclick=function(){			var oli=document.createElement(&quot;li&quot;);			oli.innerHTML=otxt.value;			otxt.value=&quot;&quot;;			if(oul.children.length&gt;0)				oul.insertBefore(oli,oul.children[0]);			else				oul.appendChild(oli);			//运动			var iheight=oli.offsetHeight;			alert(iheight);			oli.style.height=&quot;0&quot;;			move(oli,{height:iheight});		};	};		function getStyle(obj,attr){		if(obj.currentStyle)			return obj.currentStyle[attr];		else			return getComputedStyle(obj,false)[attr];	}	function move(obj,json,fun){		clearInterval(obj.timer);		obj.timer=setInterval(function(){			var astop=true;			for(var attr in json){				var cur=0;				if(attr==&quot;opacity&quot;)					cur=Math.round(parseFloat(getStyle(obj,attr))*100);				else					cur=parseInt(getStyle(obj,attr));				var speed=(json[attr]-cur)/10;				speed=speed&gt;0?Math.ceil(speed):Math.floor(speed);				if(cur!=json[attr])					astop=false;				if(attr==&quot;opacity&quot;){					if(obj.style.filter)						obj.style.filter=&quot;alpha(opacity:&quot;+(speed+cur)+&quot;)&quot;;					else						obj.style.opacity=(speed+cur)/100;				}				else					obj.style[attr]=speed+cur+&quot;px&quot;;			}			if(astop){				clearInterval(obj.timer);				if(fun)					fun();			}		},30);	}&lt;/script&gt;&lt;/head&gt;&lt;body&gt;	&lt;div id=&quot;div1&quot;&gt;		&lt;form&gt;			&lt;textarea id=&quot;text1&quot;&gt;&lt;/textarea&gt;			&lt;input type=&quot;button&quot; value=&quot;发布&quot; id=&quot;btn&quot;/&gt;		&lt;/form&gt;	&lt;/div&gt;	&lt;div id=&quot;div2&quot;&gt;		&lt;ul id=&quot;ul1&quot;&gt;		&lt;/ul&gt;	&lt;/div&gt;&lt;/body&gt;&lt;/html&gt;

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Reply to the discussion (solution)

What’s the problem

After reading it for a long time I don’t understand what you are asking

What’s the problem

The padding on the top and bottom of ul is the same, but the space below is obviously larger than the top

After reading for a long time, I didn’t understand what you were asking.

The padding on the top and bottom of ul is the same, but the space below is obviously larger than the top

This is the height definition of offsetHeight and the box- of li sizing is caused by the conflict of content-box

The offsetHeight property returns the viewable height of an element in pixels, including padding, border and scrollbar
That is to say, offsetHeight contains content, padding-top, padding- bottom, border-top, border-bottom, and the height involving scrollbar
box-sizing: the height of the content-box specified element only contains the content, and not others.
In your code, after the height of li is reset, and the sum of padding-top and padding-bottom is always more than expected.
After that, padding-top and padding-bottom have not changed, they are both the 10px you specified, and this extra Part is added to the height of content, but the font of content does not become larger, and the text is not processed to be vertically centered in content, so it looks like the top and bottom spaces are different

So you can add the following CSS, when scrollbar does not exist, it can be solved

li{    box-sizing: border-box;}

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The definition of box-sizing on W3C is quoted

3.1. box-sizing property

Name: box-sizing
Value: content-box | border-box
Initial: content-box

content-box
This is the behavior of width and height as specified by CSS2.1. The specified width and height (and respective min/max properties) apply to the width and height respectively of the content box of the element. The padding and border of the element are laid out and drawn outside the specified width and height .

border-box
Length and percentages values for width and height (and respective min/max properties) on this element determine the border box of the element. That is, any padding or border specified on the element is laid out and drawn inside this specified width and height. The content width and height are calculated by subtracting the border and padding widths of the relevant sides from the specified width and height properties. As the content width and height cannot be be negative ([ CSS21], section 10.2), this computation is floored at 0. Used values, as exposed for instance through getComputedStyle(), also refer to the border box.

This definition indicates the default of box-sizing The value is content-box; the value of box-sizing will affect the definition of height in css - whether the padding and border in the vertical direction will be included in height

W3C 上 box-sizing 的定义引用

3.1. box-sizing property

Name: box-sizing
Value: content-box | border-box
Initial: content-box

content-box
This is the behavior of width and height as specified by CSS2.1. The specified width and height (and respective min/max properties) apply to the width and height respectively of the content box of the element. The padding and border of the element are laid out and drawn outside the specified width and height.

border-box
Length and percentages values for width and height (and respective min/max properties) on this element determine the border box of the element. That is, any padding or border specified on the element is laid out and drawn inside this specified width and height. The content width and height are calculated by subtracting the border and padding widths of the respective sides from the specified width and height properties. As the content width and height cannot be negative ([CSS21], section 10.2), this computation is floored at 0. Used values, as exposed for instance through getComputedStyle(), also refer to the border box.

这个定义表明 box-sizing 的默认值是 content-box; box-sizing 的值将影响 css 中 height 的定义-- 垂直方向上的 padding 和 border 究竟会不会包含在 height 中

W3C 上 box-sizing 的定义引用

3.1. box-sizing property

Name: box-sizing
Value: content-box | border-box
Initial: content-box

content-box
This is the behavior of width and height as specified by CSS2.1. The specified width and height (and respective min/max properties) apply to the width and height respectively of the content box of the element. The padding and border of the element are laid out and drawn outside the specified width and height.

border-box
Length and percentages values for width and height (and respective min/max properties) on this element determine the border box of the element. That is, any padding or border specified on the element is laid out and drawn inside this specified width and height. The content width and height are calculated by subtracting the border and padding widths of the respective sides from the specified width and height properties. As the content width and height cannot be negative ([CSS21], section 10.2), this computation is floored at 0. Used values, as exposed for instance through getComputedStyle(), also refer to the border box.

这个定义表明 box-sizing 的默认值是 content-box; box-sizing 的值将影响 css 中 height 的定义-- 垂直方向上的 padding 和 border 究竟会不会包含在 height 中

但是如果出现了滚动条，页面就会变成这个样子

看了半天没看懂你问的是什么

ul上下的padding一样，但是下面的空白明显大于上面

你这里又给他加了高度

//运动            var iheight=oli.offsetHeight;            alert(iheight);            oli.style.height=&quot;0&quot;;            move(oli,{height:iheight});

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但是如果出现了滚动条，页面就会变成这个样子

我分别在 Chrome 42, IE8, Firefox 39.0 测试, 只发现 Firefox 存在这个问题

下面多余的部分不全是padding，还有一部分是li的高。
oli.offsetHeight获取的值是包括padding在内的，但是oli.style.height这样赋值的高是不包括padding的。
最简单的解决方法就是减掉padding，即var iheight=oli.offsetHeight-20;
但这样解决效果不太好，因为oli.style.height=“0”;时其实padding部分还是看的见的。
要效果好，也要简单就用jquery吧，修改如下

&lt;script src=&quot;http://code.jquery.com/jquery-1.8.3.min.js&quot;&gt;&lt;/script&gt;&lt;!--+++++++++++++加载jquery++++++++++++++--&gt;&lt;script type=&quot;text/javascript&quot;&gt;    window.onload=function(){        var adiv1=document.getElementById(&quot;div1&quot;);        var adiv2=document.getElementById(&quot;div2&quot;);        var obtn=adiv1.getElementsByTagName(&quot;input&quot;)[0];        var otxt=adiv1.getElementsByTagName(&quot;textarea&quot;)[0];        var oul=document.getElementById(&quot;ul1&quot;);        obtn.onclick=function(){            var oli=document.createElement(&quot;li&quot;);            oli.style.display=&quot;none&quot;;//+++++++++++++++++++++先隐藏++++++++++++++++++++            oli.innerHTML=otxt.value;            otxt.value=&quot;&quot;;            if(oul.children.length&gt;0)                oul.insertBefore(oli,oul.children[0]);            else                oul.appendChild(oli);            $(oli).slideDown(800);//++++++++++++++++用jquery方法展开li++++++++++++++++++++            /*-------------------------------这段不需要了------------------------------------------            //运动            var iheight=oli.offsetHeight-20;            alert(iheight);            oli.style.height=&quot;0&quot;;            move(oli,{height:iheight});            */        };    };&lt;/script&gt;

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但是如果出现了滚动条，页面就会变成这个样子

仅在 Firefox 中发现这个问题

原因已经证实:

当 div2 出现垂直滚动条时, 将压缩 ul 和 li 的宽度, 而每一个 li 内容没有发生变化, 当宽度减小时, 其中文字占用的行数就有可能增加, 这样就需要更大的 height 才能容纳, 此时 Chrome, IE 都忽略了 height 被设成的固定的值, 而是将它重新计算并调整;
但 Firefox 的处理方式却不一样, 它没有忽略 height 那个已被设定的固定的值, 而是维持那个值, 不做重新计算并调整, 所以就造成最后文本超出边界的问题. 而最新插入的 li 是在插入的时候(无论有(已有/将有)无滚动条)自动计算出的 height, 所以唯一最新的 li 不会存在文本超出边界的问题.

解决方案:

在每一次插入新的 li 之前, 将上一个 li 的 height 恢复为浏览器自动计算

经测试, Chrome 42, IE8, Firefox 39.0 都没有问题

&lt;!DOCTYPE html PUBLIC &quot;-//W3C//DTD XHTML 1.0 Transitional//EN&quot; &quot;http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd&quot;&gt;&lt;html xmlns=&quot;http://www.w3.org/1999/xhtml&quot;&gt;&lt;head&gt;&lt;meta http-equiv=&quot;Content-Type&quot; content=&quot;text/html; charset=gb2312&quot; /&gt;&lt;title&gt;无标题文档&lt;/title&gt;&lt;style&gt;	body,div,dl,dt,dd,ul,ol,li,h1,h2,h3,h4,h5,h6,pre,form,fieldset,input,textarea,p,blockquote,th,td,img {padding:0;margin:0;} 	#div1{		margin:10px;		width:300px;		height:200px;	}	#div1 textarea{		width:300px;		height:180px;	}	#div2{		margin:10px auto;		height:400px;		width:400px;		border:1px solid black;		overflow:auto;	}	#div2 ul li{		border-bottom:1px dashed black;		list-style:none;		padding:10px 10px 10px 10px;		box-sizing: border-box;	}&lt;/style&gt;&lt;script type=&quot;text/javascript&quot;&gt;	window.onload=function(){		var adiv1=document.getElementById(&quot;div1&quot;);		var adiv2=document.getElementById(&quot;div2&quot;);		var obtn=adiv1.getElementsByTagName(&quot;input&quot;)[0];		var otxt=adiv1.getElementsByTagName(&quot;textarea&quot;)[0];		var oul=document.getElementById(&quot;ul1&quot;);		obtn.onclick=function(){			var oli=document.createElement(&quot;li&quot;);			oli.innerHTML=otxt.value;			otxt.value=&quot;&quot;;			if(oul.children.length&gt;0) {                oul.children[0].style.height = 'auto'; // 将上一个 li 的 height 恢复为浏览器自动计算				oul.insertBefore(oli,oul.children[0]);			} else				oul.appendChild(oli);			//运动			var iheight=oli.offsetHeight;			alert(iheight);			oli.style.height=&quot;0&quot;;			move(oli,{height:iheight});		};	};		function getStyle(obj,attr){		if(obj.currentStyle)			return obj.currentStyle[attr];		else			return getComputedStyle(obj,false)[attr];	}	function move(obj,json,fun){		clearInterval(obj.timer);		obj.timer=setInterval(function(){			var astop=true;			for(var attr in json){				var cur=0;				if(attr==&quot;opacity&quot;)					cur=Math.round(parseFloat(getStyle(obj,attr))*100);				else					cur=parseInt(getStyle(obj,attr));				var speed=(json[attr]-cur)/10;				speed=speed&gt;0?Math.ceil(speed):Math.floor(speed);				if(cur!=json[attr])					astop=false;				if(attr==&quot;opacity&quot;){					if(obj.style.filter)						obj.style.filter=&quot;alpha(opacity:&quot;+(speed+cur)+&quot;)&quot;;					else						obj.style.opacity=(speed+cur)/100;				}				else					obj.style[attr]=speed+cur+&quot;px&quot;;			}			if(astop){				clearInterval(obj.timer);				if(fun)					fun();			}		},30);	}&lt;/script&gt;&lt;/head&gt;&lt;body&gt;	&lt;div id=&quot;div1&quot;&gt;		&lt;form&gt;			&lt;textarea id=&quot;text1&quot;&gt;&lt;/textarea&gt;			&lt;input type=&quot;button&quot; value=&quot;发布&quot; id=&quot;btn&quot;/&gt;		&lt;/form&gt;	&lt;/div&gt;	&lt;div id=&quot;div2&quot;&gt;		&lt;ul id=&quot;ul1&quot;&gt;		&lt;/ul&gt;	&lt;/div&gt;&lt;/body&gt;&lt;/html&gt;

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看了半天没看懂你问的是什么

ul上下的padding一样，但是下面的空白明显大于上面

你这里又给他加了高度

//运动            var iheight=oli.offsetHeight;            alert(iheight);            oli.style.height=&quot;0&quot;;            move(oli,{height:iheight});

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这儿是为了实现一个滑动效果，和padding没关系吧，何况最终的高度并没有改变

但是如果出现了滚动条，页面就会变成这个样子

我分别在 Chrome 42, IE8, Firefox 39.0 测试, 只发现 Firefox 存在这个问题

chrome43，IE11也存在问题

&lt;script src=&quot;http://code.jquery.com/jquery-1.8.3.min.js&quot;&gt;&lt;/script&gt;&lt;!--+++++++++++++加载jquery++++++++++++++--&gt;&lt;script type=&quot;text/javascript&quot;&gt;    window.onload=function(){        var adiv1=document.getElementById(&quot;div1&quot;);        var adiv2=document.getElementById(&quot;div2&quot;);        var obtn=adiv1.getElementsByTagName(&quot;input&quot;)[0];        var otxt=adiv1.getElementsByTagName(&quot;textarea&quot;)[0];        var oul=document.getElementById(&quot;ul1&quot;);        obtn.onclick=function(){            var oli=document.createElement(&quot;li&quot;);            oli.style.display=&quot;none&quot;;//+++++++++++++++++++++先隐藏++++++++++++++++++++            oli.innerHTML=otxt.value;            otxt.value=&quot;&quot;;            if(oul.children.length&gt;0)                oul.insertBefore(oli,oul.children[0]);            else                oul.appendChild(oli);            $(oli).slideDown(800);//++++++++++++++++用jquery方法展开li++++++++++++++++++++            /*-------------------------------这段不需要了------------------------------------------            //运动            var iheight=oli.offsetHeight-20;            alert(iheight);            oli.style.height=&quot;0&quot;;            move(oli,{height:iheight});            */        };    };&lt;/script&gt;

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是的，我不用offsetHeight就可以了
可以用

function getStyle(obj,attr){		if(obj.currentStyle)			return obj.currentStyle[attr];		else			return getComputedStyle(obj,false)[attr];	}

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这个函数来获取li的高度就不会包括padding
谢谢，问题解决了！

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