关于reset.css的疑问:为什么一定要重置浏览器样式?
自开始做前端算起,我所做过的每一个项目中都会有一个reset.css,也就是重置样式表。我现在想想都不知道第一次是从哪儿弄来的一个重置样式表。快五年了,好像从来都没有质疑过关于重置样式表的内容。
这样一个样式表里往往会有一大段对“浏览器样式”的清除与重置。刚开始做前端的时候一度感觉,能写出来这么一个样式表似乎很酷、很牛;做时间久了,也自己开始针对不同项目写自己的reset.css了,但也不外乎是一大堆重置样式,有时候都不关心浏览器里每个元素有什么样的默认样式,只是唯恐漏掉哪个元素没有把样式重置掉;其实在添加的的一些标签里,都不知道浏览器的默认样式是什么就一味的添进去了。只是感觉好酷,汗~
到了今天,感觉好多东西,似乎有点追求形式了。查了好多关于浏览器默认样式的资料以后,发现我们写的一大堆重置样式里好多其实不需要重置,而且似乎根本不明白重置的原因与目的。于是我开始查reset的来源,后来在张鑫旭的博客里看到了这么一段内容:
1. div,address标签默认有margin值吗?有padding值吗?怎么会想到应用address,div{margin:0; padding:0;}属性呢?真是画蛇添足,多此一举。
2. dt标签有默认的margin与padding值就是0,这里为什么还要使用呢?
3. li标签默认有margin值吗?有padding值吗?压根就没有,也不自己测测,还没事找事设置个li{margin:0; padding:0;}属性,真是衰!
4. code标签是个属于inline水平的元素,居然也扯到margin与padding的重置,真是好笑。
5. fieldset, legend这两个90年代的标签你的网站上使用了吗?使用概率不足1%的标签也拿来重置,我实在无语了。
6. 还有th,td这些标签,幸好没有写上table与tr标签,否则我一起痛批一段。
另:经测试article, aside, footer, header, hgroup, main, nav, section, dt, summary, details这些标签也没有默认的margin与padding值。
据淘宝的射雕的叙述,最早的一份CSS resest来自Tantek 的undohtml.css,很简单的代码,Tantek 根据自己的需要,对浏览器的默认样式进行了一些重置。其余一些有名的CSS reset如业界领袖Eric Meyer的reset,或是Tripoli Reset。
这里附上undohtml.css:
@charset "utf-8"; /* CSS Document */ /* undohtml.css @author:Tantek */ /* (CC) 2004 Tantek Celik. Some Rights Reserved. */ /* http://creativecommons.org/licenses/by/2.0 */ /* This style sheet is licensed under a Creative Commons License. */ /* Purpose: undo some of the default styling of common (X)HTML browsers */ /* link underlines tend to make hypertext less readable, because underlines obscure the shapes of the lower halves of words */ :link,:visited { text-decoration:none } /* no list-markers by default, since lists are used more often for semantics */ ul,ol { list-style:none } /* avoid browser default inconsistent heading font-sizes */ /* and pre/code too */ h1,h2,h3,h4,h5,h6,pre,code { font-size:1em; } /* remove the inconsistent (among browsers) default ul,ol padding or margin */ /* the default spacing on headings does not match nor align with normal interline spacing at all, so let‘s get rid of it. */ /* zero out the spacing around pre, form, body, html, p, blockquote as well */ /* form elements are oddly inconsistent, and not quite CSS emulatable. */ /* nonetheless strip their margin and padding as well */ ul,ol,li,h1,h2,h3,h4,h5,h6,pre,form,body,html,p,blockquote,fieldset,input { margin:0; padding:0 } /* whoever thought blue linked image borders were a good idea? */ a img,:link img,:visited img { border:none } /* de-italicize address */ address { font-style:normal } /* more varnish stripping as necessary... */
CSS reset的作用是让各个浏览器的CSS样式有一个统一的基准,而这个基准更多的就是“清零”。但“清零”的目的是避免不同浏览器有不同的默认样式而导致有bug产生;所以,有时候我们对很多标签做的一些清零,其实是没什么意义的,说的不好听一点,是盲目跟风。
张鑫旭认为css reset应该是这样的:
body, dl, dd, h1, h2, h3, h4, h5, h6, p, form{margin:0;} ol,ul{margin:0; padding:0;}
我也觉得这些足够了。其余的中在样式里原本就可以设置了,不然会多出很多重置的样式,徒增样式量,毫无用处。
鉴于没有实践就没有发言权的说法,我自己测试了一下chrome浏览器的默认样式(有大把自由时间的童鞋们,也去自己测试一下收获颇丰~):
@charset "utf-8"; /* chrome default CSS Document */ html, address, div, p, article, aside, footer, header, hgroup, main, nav, section, dt, summary, details, figcaption, frameset, frame{display:block;} head, meta, title, link, style, script, datalist, noframes{display:none;} map, area, output, q{display:inline;} {display:none;} body{display:block;margin:8px;} a:-webkit-any-link{ color:-webkit-link; text-decoration:underline; cursor:auto; } /*无样式的标签: abbr,acronym(HTML不支持此标签),img, base, basefont, br, canvas, embed, font, noscript, object, span, time, wbr */ pre, xmp, plaintext, listing { display: block; font-family: monospace; white-space: pre; margin: 1em 0px; } mark { background-color: yellow; color: black; } sub { vertical-align: sub; font-size: smaller; } sup { vertical-align: super; font-size: smaller; } i, cite, em, var, address, dfn{ font-style:italic; } strong, b { font-weight: bold; } /*address{ display:block; }*/ center { display: block; text-align: -webkit-center; } u, ins { text-decoration: underline; } s, strike, del { text-decoration: line-through; } big { font-size: larger; } small { font-size: smaller; } bdi, output { /*//////////////////////////////////////////////////////////*/ unicode-bidi: -webkit-isolate; } /*output { display: inline; }*/ /*q { display: inline; }*/ q::before { content: open-quote; } q::after { content: close-quote; } ruby, rt { text-indent: 0px; } rt { line-height: normal; -webkit-text-emphasis: none; } ruby > rp { /*rt、rp:一个ruby注释*/ display: none; } bdo { unicode-bidi: bidi-override; } tt, code, kbd, samp { font-family: monospace; } blockquote { display: block; -webkit-margin-before: 1em; -webkit-margin-after: 1em; -webkit-margin-start: 40px; -webkit-margin-end: 40px; } p{ display:block; -webkit-margin-before:1em; -webkit-margin-after:1em; -webkit-margin-start:0px; -webkit-margin-end:0px; } audio { width: 300px; height: 30px; } video { object-fit: contain; } audio::-webkit-media-controls-timeline, video::-webkit-media-controls-timeline { -webkit-appearance: media-slider; display: flex; flex: 1 1 auto; height: 8px; margin: 0px 15px 0px 0px; padding: 0px; background-color: transparent; min-width: 25px; border: initial; color: inherit; } form { display: block; margin-top: 0em; } /*datalist{ display:none; }*/ input[type="range" i] { -webkit-appearance: slider-horizontal; padding: initial; border: initial; margin: 2px; color: rgb(144, 144, 144); } input, input[type="password" i], input[type="search" i] { -webkit-appearance: textfield; padding: 1px; background-color: white; border: 2px inset; border-image-source: initial; border-image-slice: initial; border-image-width: initial; border-image-outset: initial; border-image-repeat: initial; -webkit-rtl-ordering: logical; -webkit-user-select: text; cursor: auto; } input[type="button" i], input[type="submit" i], input[type="reset" i], input[type="file" i]::-webkit-file-upload-button, button { align-items: flex-start; text-align: center; cursor: default; color: buttontext; padding: 2px 6px 3px; border: 2px outset buttonface; border-image-source: initial; border-image-slice: initial; border-image-width: initial; border-image-outset: initial; border-image-repeat: initial; background-color: buttonface; box-sizing: border-box; } input, textarea, keygen, select, button { margin: 0em; font: -webkit-small-control; color: initial; letter-spacing: normal; word-spacing: normal; text-transform: none; text-indent: 0px; text-shadow: none; display: inline-block; text-align: start; } input, textarea, keygen, select, button, meter, progress { -webkit-writing-mode: horizontal-tb; } textarea { font-family: monospace; border-color: rgb(169, 169, 169); } textarea { -webkit-appearance: textarea; background-color: white; border: 1px solid; border-image-source: initial; border-image-slice: initial; border-image-width: initial; border-image-outset: initial; border-image-repeat: initial; -webkit-rtl-ordering: logical; -webkit-user-select: text; flex-direction: column; resize: auto; cursor: auto; padding: 2px; white-space: pre-wrap; word-wrap: break-word; } progress { -webkit-appearance: progress-bar; box-sizing: border-box; display: inline-block; height: 1em; width: 10em; vertical-align: -0.2em; } meter { -webkit-appearance: meter; box-sizing: border-box; display: inline-block; height: 1em; width: 5em; vertical-align: -0.2em; } button { -webkit-appearance: button; } select { -webkit-appearance: menulist; box-sizing: border-box; align-items: center; border: 1px solid; border-image-source: initial; border-image-slice: initial; border-image-width: initial; border-image-outset: initial; border-image-repeat: initial; white-space: pre; -webkit-rtl-ordering: logical; color: black; background-color: white; cursor: default; } optgroup { font-weight: bolder; display: block; } option { font-weight: normal; display: block; padding: 0px 2px 1px; white-space: pre; min-height: 1.2em; font: inherit; } keygen, select { border-radius: 5px; } keygen, select, select[size="0"], select[size="1"] { border-radius: 0px; border-color: rgb(169, 169, 169); } label { cursor: default; } table { display: table; border-collapse: separate; border-spacing: 2px; border-color: gray; } caption { display: table-caption; text-align: -webkit-center; } tbody { display: table-row-group; vertical-align: middle; border-color: inherit; } tfoot { display: table-footer-group; vertical-align: middle; border-color: inherit; } tr { display: table-row; vertical-align: inherit; border-color: inherit; } td, th { display: table-cell; vertical-align: inherit; } th { font-weight: bold; } colgroup { display: table-column-group; } col { display: table-column; } dialog { position: absolute; left: 0px; right: 0px; width: -webkit-fit-content; height: -webkit-fit-content; margin: auto; border: solid; border-image-source: initial; border-image-slice: initial; border-image-width: initial; border-image-outset: initial; border-image-repeat: initial; padding: 1em; background: white; color: black; } dialog::backdrop { position: fixed; top: 0px; right: 0px; bottom: 0px; left: 0px; background: rgba(0, 0, 0, 0.0980392); } ul, menu, dir { display: block; list-style-type: disc; -webkit-margin-before: 1em; -webkit-margin-after: 1em; -webkit-margin-start: 0px; -webkit-margin-end: 0px; -webkit-padding-start: 40px; } ol { display: block; list-style-type: decimal; -webkit-margin-before: 1em; -webkit-margin-after: 1em; -webkit-margin-start: 0px; -webkit-margin-end: 0px; -webkit-padding-start: 40px; } li { display: list-item; text-align: -webkit-match-parent; } dl { display: block; -webkit-margin-before: 1em; -webkit-margin-after: 1em; -webkit-margin-start: 0px; -webkit-margin-end: 0px; } /*dt { display: block; }*/ dd { display: block; -webkit-margin-start: 40px; } fieldset { display: block; -webkit-margin-start: 2px; -webkit-margin-end: 2px; -webkit-padding-before: 0.35em; -webkit-padding-start: 0.75em; -webkit-padding-end: 0.75em; -webkit-padding-after: 0.625em; border: 2px groove threedface; border-image-source: initial; border-image-slice: initial; border-image-width: initial; border-image-outset: initial; border-image-repeat: initial; min-width: -webkit-min-content; } legend { display: block; -webkit-padding-start: 2px; -webkit-padding-end: 2px; border: none; border-image-source: initial; border-image-slice: initial; border-image-width: initial; border-image-outset: initial; border-image-repeat: initial; } figure { display: block; -webkit-margin-before: 1em; -webkit-margin-after: 1em; -webkit-margin-start: 40px; -webkit-margin-end: 40px; } figcaption { display: block; } frameset { border-color: inherit; } /*frameset, frame { display: block; }*/ h1 { display: block; font-size: 2em; -webkit-margin-before: 0.67em; -webkit-margin-after: 0.67em; -webkit-margin-start: 0px; -webkit-margin-end: 0px; font-weight: bold; } :-webkit-any(article,aside,nav,section) h1 { font-size: 1.5em; -webkit-margin-before: 0.83em; -webkit-margin-after: 0.83em; } h2 { display: block; font-size: 1.5em; -webkit-margin-before: 0.83em; -webkit-margin-after: 0.83em; -webkit-margin-start: 0px; -webkit-margin-end: 0px; font-weight: bold; } h3 { display: block; font-size: 1.17em; -webkit-margin-before: 1em; -webkit-margin-after: 1em; -webkit-margin-start: 0px; -webkit-margin-end: 0px; font-weight: bold; } h4 { display: block; -webkit-margin-before: 1.33em; -webkit-margin-after: 1.33em; -webkit-margin-start: 0px; -webkit-margin-end: 0px; font-weight: bold; } h5 { display: block; font-size: 0.83em; -webkit-margin-before: 1.67em; -webkit-margin-after: 1.67em; -webkit-margin-start: 0px; -webkit-margin-end: 0px; font-weight: bold; } h6 { display: block; font-size: 0.67em; -webkit-margin-before: 2.33em; -webkit-margin-after: 2.33em; -webkit-margin-start: 0px; -webkit-margin-end: 0px; font-weight: bold; } hr { display: block; -webkit-margin-before: 0.5em; -webkit-margin-after: 0.5em; -webkit-margin-start: auto; -webkit-margin-end: auto; border-style: inset; border-width: 1px; } iframe { border: 2px inset; border-image-source: initial; border-image-slice: initial; border-image-width: initial; border-image-outset: initial; border-image-repeat: initial; }
另附上通过查找到的资料总结的一些浏览器的margin值与padding值(没有一一测试,有兴趣的可以自己测试一下):
IE-7: 有默认外边距margin样式的元素: dd,menu, ol, ul, blockquote, body, dd, dl, form, h1-6, ul 有默认内边距padding样式的元素: th, td, textarea, input, fieldset, caption, IE-8: 有默认外边距margin样式的元素: dd, menu, ol, ul, blockquote, body, dd, dl,fieldset, h1-6, hr, p, pre, 有默认内边距padding样式的元素: ul, th, textarea, td, ol, menu, legend, input, fieldset, button, [dir=rtl] ul, [dir=rtl] ol, [dir=rtl] menu IE-9: 有默认外边距margin样式的元素(与IE-8的默认样式一样): dd, menu, ol, ul, blockquote, body, dd, dl, fieldset, h1-6, hr, p, pre, 有默认内边距padding样式的元素: ul, th, textarea, td, ol, menu, legend, input, fieldset, button, [dir=rtl] ul, [dir=rtl] ol, [dir=rtl] menu webkit:(ol ul, ul ol, ul ul, ol ol{margin-top:0;margin-bottom:0;}), 有默认外边距margin样式的元素: body, p, blockquote, hr, h1-6, ul, ol, menu, dir, dd(margin-start), dl, form, fieldset, input, textarea, keygen, select, button, isindex, datagrid, pre, xmp, plaintext, listing, 有默认内边距padding样式的元素: input, textarea, fieldset, legend opera: 有默认外边距margin样式的元素: body, blockquote, dd, dl, fieldset, h1-6, hr, menu, p, pre, ul 有默认内边距padding样式的元素: ul, th, td, textarea, select, ol, menu, legend, keygen, input, fieldset, button, address,
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