从 normalize.css 分析 CSS Reset

为什么要进行 `CSS Reset`

目的简单而又粗暴：使CSS样式在各种浏览器下呈现的效果一样。

当年的一个~~黑魔法~~：

1	* { margin: 0; padding: 0; }

这种粗暴的方式曾经给浏览器带来了很大的负荷，它由曾经的红极一时变成现在不受待见。

后来有了一个更加飘逸的CSS Reset代码，它是这样写的：

1	body, div, dl, dt, dd, ul, ol, li, h1, h2, h3, h4, h5, h6, pre, code, form, fieldset, legend, input, button, textarea, p, blockquote, th, td { margin: 0;padding: 0; }

更有甚者，将前面一堆CSS选择器换成了几乎所有HTML标签，与上一个黑魔法并无二致。

这里引用一下张鑫旭的吐槽：

div标签默认有margin值吗？有padding值吗？怎么会想到应用div{margin:0; padding:0;}属性呢？真是画蛇添足，多此一举。

dt标签有默认的margin与padding值就是0，这里为什么还要使用呢？

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！

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。

还有，像form, input, button, textarea这样子的表单元素，有margin值吗？有padding值吗？我真是不解！

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。

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。

normalize.css是什么？

normalize.css是一个CSS Reset项目，由necolas发起并维护。

以下部分文字为normalize.css官网的介绍：

A modern, HTML5-ready alternative to CSS resets

Normalize.css makes browsers render all elements more consistently and in line with modern standards. It precisely targets only the styles that need normalizing.

知乎上有一段针对normalize.css 的评价：

Normalize 相对「平和」，注重通用的方案，重置掉该重置的样式，保留有用的 user agent 样式，同时进行一些 bug 的修复，这点是 reset 所缺乏的。

参考资料

`normalize.css v4.1.1` 源码

/*! normalize.css v4.1.1 | MIT License | github.com/necolas/normalize.css */

/**
 * 1. Change the default font family in all browsers (opinionated).
 * 2. Prevent adjustments of font size after orientation changes in IE and iOS.
 */

html {
  font-family: sans-serif; /* 1 */
  -ms-text-size-adjust: 100%; /* 2 */
  -webkit-text-size-adjust: 100%; /* 2 */
}

/**
 * Remove the margin in all browsers (opinionated).
 */

body {
  margin: 0;
}

/* HTML5 display definitions
   ========================================================================== */

/**
 * Add the correct display in IE 9-.
 * 1. Add the correct display in Edge, IE, and Firefox.
 * 2. Add the correct display in IE.
 */

article,
aside,
details, /* 1 */
figcaption,
figure,
footer,
header,
main, /* 2 */
menu,
nav,
section,
summary { /* 1 */
  display: block;
}

/**
 * Add the correct display in IE 9-.
 */

audio,
canvas,
progress,
video {
  display: inline-block;
}

/**
 * Add the correct display in iOS 4-7.
 */

audio:not([controls]) {
  display: none;
  height: 0;
}

/**
 * Add the correct vertical alignment in Chrome, Firefox, and Opera.
 */

progress {
  vertical-align: baseline;
}

/**
 * Add the correct display in IE 10-.
 * 1. Add the correct display in IE.
 */

template, /* 1 */
[hidden] {
  display: none;
}

/* Links
   ========================================================================== */

/**
 * 1. Remove the gray background on active links in IE 10.
 * 2. Remove gaps in links underline in iOS 8+ and Safari 8+.
 */

a {
  background-color: transparent; /* 1 */
  -webkit-text-decoration-skip: objects; /* 2 */
}

/**
 * Remove the outline on focused links when they are also active or hovered
 * in all browsers (opinionated).
 */

a:active,
a:hover {
  outline-width: 0;
}

/* Text-level semantics
   ========================================================================== */

/**
 * 1. Remove the bottom border in Firefox 39-.
 * 2. Add the correct text decoration in Chrome, Edge, IE, Opera, and Safari.
 */

abbr[title] {
  border-bottom: none; /* 1 */
  text-decoration: underline; /* 2 */
  text-decoration: underline dotted; /* 2 */
}

/**
 * Prevent the duplicate application of `bolder` by the next rule in Safari 6.
 */

b,
strong {
  font-weight: inherit;
}

/**
 * Add the correct font weight in Chrome, Edge, and Safari.
 */

b,
strong {
  font-weight: bolder;
}

/**
 * Add the correct font style in Android 4.3-.
 */

dfn {
  font-style: italic;
}

/**
 * Correct the font size and margin on `h1` elements within `section` and
 * `article` contexts in Chrome, Firefox, and Safari.
 */

h1 {
  font-size: 2em;
  margin: 0.67em 0;
}

/**
 * Add the correct background and color in IE 9-.
 */

mark {
  background-color: #ff0;
  color: #000;
}

/**
 * Add the correct font size in all browsers.
 */

small {
  font-size: 80%;
}

/**
 * Prevent `sub` and `sup` elements from affecting the line height in
 * all browsers.
 */

sub,
sup {
  font-size: 75%;
  line-height: 0;
  position: relative;
  vertical-align: baseline;
}

sub {
  bottom: -0.25em;
}

sup {
  top: -0.5em;
}

/* Embedded content
   ========================================================================== */

/**
 * Remove the border on images inside links in IE 10-.
 */

img {
  border-style: none;
}

/**
 * Hide the overflow in IE.
 */

svg:not(:root) {
  overflow: hidden;
}

/* Grouping content
   ========================================================================== */

/**
 * 1. Correct the inheritance and scaling of font size in all browsers.
 * 2. Correct the odd `em` font sizing in all browsers.
 */

code,
kbd,
pre,
samp {
  font-family: monospace, monospace; /* 1 */
  font-size: 1em; /* 2 */
}

/**
 * Add the correct margin in IE 8.
 */

figure {
  margin: 1em 40px;
}

/**
 * 1. Add the correct box sizing in Firefox.
 * 2. Show the overflow in Edge and IE.
 */

hr {
  box-sizing: content-box; /* 1 */
  height: 0; /* 1 */
  overflow: visible; /* 2 */
}

/* Forms
   ========================================================================== */

/**
 * 1. Change font properties to `inherit` in all browsers (opinionated).
 * 2. Remove the margin in Firefox and Safari.
 */

button,
input,
optgroup,
select,
textarea {
  font: inherit; /* 1 */
  margin: 0; /* 2 */
}

/**
 * Restore the font weight unset by the previous rule.
 */

optgroup {
  font-weight: bold;
}

/**
 * Show the overflow in IE.
 * 1. Show the overflow in Edge.
 */

button,
input { /* 1 */
  overflow: visible;
}

/**
 * Remove the inheritance of text transform in Edge, Firefox, and IE.
 * 1. Remove the inheritance of text transform in Firefox.
 */

button,
select { /* 1 */
  text-transform: none;
}

/**
 * 1. Prevent a WebKit bug where (2) destroys native `audio` and `video`
 *    controls in Android 4.
 * 2. Correct the inability to style clickable types in iOS and Safari.
 */

button,
html [type="button"], /* 1 */
[type="reset"],
[type="submit"] {
  -webkit-appearance: button; /* 2 */
}

/**
 * Remove the inner border and padding in Firefox.
 */

button::-moz-focus-inner,
[type="button"]::-moz-focus-inner,
[type="reset"]::-moz-focus-inner,
[type="submit"]::-moz-focus-inner {
  border-style: none;
  padding: 0;
}

/**
 * Restore the focus styles unset by the previous rule.
 */

button:-moz-focusring,
[type="button"]:-moz-focusring,
[type="reset"]:-moz-focusring,
[type="submit"]:-moz-focusring {
  outline: 1px dotted ButtonText;
}

/**
 * Change the border, margin, and padding in all browsers (opinionated).
 */

fieldset {
  border: 1px solid #c0c0c0;
  margin: 0 2px;
  padding: 0.35em 0.625em 0.75em;
}

/**
 * 1. Correct the text wrapping in Edge and IE.
 * 2. Correct the color inheritance from `fieldset` elements in IE.
 * 3. Remove the padding so developers are not caught out when they zero out
 *    `fieldset` elements in all browsers.
 */

legend {
  box-sizing: border-box; /* 1 */
  color: inherit; /* 2 */
  display: table; /* 1 */
  max-width: 100%; /* 1 */
  padding: 0; /* 3 */
  white-space: normal; /* 1 */
}

/**
 * Remove the default vertical scrollbar in IE.
 */

textarea {
  overflow: auto;
}

/**
 * 1. Add the correct box sizing in IE 10-.
 * 2. Remove the padding in IE 10-.
 */

[type="checkbox"],
[type="radio"] {
  box-sizing: border-box; /* 1 */
  padding: 0; /* 2 */
}

/**
 * Correct the cursor style of increment and decrement buttons in Chrome.
 */

[type="number"]::-webkit-inner-spin-button,
[type="number"]::-webkit-outer-spin-button {
  height: auto;
}

/**
 * 1. Correct the odd appearance in Chrome and Safari.
 * 2. Correct the outline style in Safari.
 */

[type="search"] {
  -webkit-appearance: textfield; /* 1 */
  outline-offset: -2px; /* 2 */
}

/**
 * Remove the inner padding and cancel buttons in Chrome and Safari on OS X.
 */

[type="search"]::-webkit-search-cancel-button,
[type="search"]::-webkit-search-decoration {
  -webkit-appearance: none;
}

/**
 * Correct the text style of placeholders in Chrome, Edge, and Safari.
 */

::-webkit-input-placeholder {
  color: inherit;
  opacity: 0.54;
}

/**
 * 1. Correct the inability to style clickable types in iOS and Safari.
 * 2. Change font properties to `inherit` in Safari.
 */

::-webkit-file-upload-button {
  -webkit-appearance: button; /* 1 */
  font: inherit; /* 2 */
}

为什么要进行 CSS Reset

normalize.css是什么？

参考资料

normalize.css v4.1.1 源码

为什么要进行 `CSS Reset`

`normalize.css v4.1.1` 源码