一、为什么要重置CSS？

html标签在浏览器中都有各自的默认样式，比如： p 标签有上下边距，strong标签有字体加粗样式，em标签有字体倾斜样式。不同浏览器的默认样式之间也会有差别，例如ul默认带有缩进的样式，在IE 下，它的缩进是通过margin实现的，而Firefox下，它的缩进是由padding实现的。在切换页面的时候，浏览器的默认样式往往会给我们带来麻烦，影响开发效率。

二、如何重置CSS

解决的方法就是一开始就将浏览器的默认样式全部去掉，更准确说就是通过重新定义标签样式。覆盖浏览器的CSS默认属性。最最简单的说法就是把浏览器提供的默认样式覆盖掉！这就是CSS reset。

三、重置方案

1.自定义重置（博主推荐）

html,
body {
  height: 100%;
  /* 文字风格 Sans-serif 各笔画粗细相同，Serif 笔画粗细不同，monospace 等宽体，cursive草书，fantasy梦幻 */
  font-family: 'Microsoft YaHei', sans-serif, 'Helvetica Neue', Helvetica, Arial,
    '黑体', '宋体', Arial;
  -webkit-tap-highlight-color: transparent;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}
body {
  font-size: 14px;
  color: #333;
}

/* 重置各标签的默认样式 */
a,
body,
center,
cite,
code,
dd,
del,
div,
dl,
dt,
em,
fieldset,
figcaption,
figure,
footer,
form,
h1,
h2,
h3,
h4,
h5,
h6,
header,
hr,
html,
img,
input,
label,
legend,
li,
mark,
ol,
p,
section,
span,
textarea,
time,
td,
th,
ul {
  margin: 0;
  border: 0;
  padding: 0;
  font-style: normal;
  box-sizing: border-box;
  /*  自动换行 */
  word-wrap: break-word;
  /*  强制英文单词断行 */
  word-break: break-all;
}

/*  设置标签为块级分类 */
article,
aside,
details,
fieldset,
figcaption,
figure,
footer,
header,
main,
nav,
section {
  display: block;
}

/* 去除input标签的默认样式 */
button,
input,
textarea {
  -webkit-appearance: none;
  font-family: 'Microsoft YaHei', sans-serif, 'Helvetica Neue', Helvetica, Arial,
    '黑体', '宋体', Arial;
  border: 0;
  margin: 0;
  padding: 0;
  font-size: 1em;
  line-height: 1em;
  outline: none;
  background-color: transparent;
}

/*  禁止多文本框手动拖动大小 */
textarea {
  resize: none;
  -webkit-appearance: none;
}

/* 去掉按下的阴影盒子 */
input,
textarea,
a {
  -webkit-tap-highlight-color: transparent;
}

/*  清除a标签下划线 */
a,
a:visited {
  text-decoration: none;
}
a:focus,
a:active,
a:hover {
  outline: none;
}

/*  清除列表前面的点 */
ol,
li,
ul {
  list-style: none;
}

/*  清除IE下图片的边框 */
img {
  border-style: none;
  font-size: 0;
}

/*  解决chrome浏览器默认黄色背景问题 */
input:-webkit-autofill,
textarea:-webkit-autofill,
select:-webkit-autofill {
  -webkit-box-shadow: 0 0 0 1000px #fff inset;
}

/*  设置默认滚动条样式 */
::-webkit-input-placeholder {
  color: #afbdcc;
}
:-moz-placeholder {
  color: #afbdcc;
}
::-moz-placeholder {
  color: #afbdcc;
}
:-ms-input-placeholder {
  color: #afbdcc;
}
::-webkit-scrollbar {
  width: 6px;
  height: 6px;
}
::-webkit-scrollbar-track {
  background-color: #f5f5f5;
}
::-webkit-scrollbar-track-piece {
  background-color: #f5f5f5;
  border-radius: 6px;
}
::-webkit-scrollbar-thumb {
  background-color: #cccccc;
  border-radius: 6px;
}
::-webkit-scrollbar-corner {
  background-color: #f5f5f5;
}
::-webkit-resizer {
  background-repeat: no-repeat;
  background-position: bottom right;
}

2.官方推荐重置（Normalize.css）

优势：

2.1.normalize.css并不是简单的重置了所有的样式，保留标签语义化

normalize没有对所有标签采取一致的重置方式，而是有针对的修改，同时也保留了标签的语义化。

2.2.normalize.css覆盖更多的标签

这点体现在html5的标签上。

2.3.normalize.css源码，注释写的很详细

2.4.补充

资源下载地址：

Normalize.css: Make browsers render all elements more consistently.

源码如下：

/*! normalize.css v8.0.1 | MIT License | github.com/necolas/normalize.css */

/* Document
   ========================================================================== */

/**
 * 1. Correct the line height in all browsers.
 * 2. Prevent adjustments of font size after orientation changes in iOS.
 */

html {
  line-height: 1.15; /* 1 */
  -webkit-text-size-adjust: 100%; /* 2 */
}

/* Sections
   ========================================================================== */

/**
 * Remove the margin in all browsers.
 */

body {
  margin: 0;
}

/**
 * Render the `main` element consistently in IE.
 */

main {
  display: block;
}

/**
 * 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;
}

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

/**
 * 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 */
}

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

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

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

/**
 * Remove the gray background on active links in IE 10.
 */

a {
  background-color: transparent;
}

/**
 * 1. Remove the bottom border in Chrome 57-
 * 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 */
}

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

b,
strong {
  font-weight: bolder;
}

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

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

/**
 * 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;
}

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

/**
 * 1. Change the font styles in all browsers.
 * 2. Remove the margin in Firefox and Safari.
 */

button,
input,
optgroup,
select,
textarea {
  font-family: inherit; /* 1 */
  font-size: 100%; /* 1 */
  line-height: 1.15; /* 1 */
  margin: 0; /* 2 */
}

/**
 * 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;
}

/**
 * Correct the inability to style clickable types in iOS and Safari.
 */

button,
[type="button"],
[type="reset"],
[type="submit"] {
  -webkit-appearance: button;
}

/**
 * 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;
}

/**
 * Correct the padding in Firefox.
 */

fieldset {
  padding: 0.35em 0.75em 0.625em;
}

/**
 * 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 */
}

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

progress {
  vertical-align: baseline;
}

/**
 * Remove the default vertical scrollbar in IE 10+.
 */

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 in Chrome and Safari on macOS.
 */

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

/**
 * 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 */
}

/* Interactive
   ========================================================================== */

/*
 * Add the correct display in Edge, IE 10+, and Firefox.
 */

details {
  display: block;
}

/*
 * Add the correct display in all browsers.
 */

summary {
  display: list-item;
}

/* Misc
   ========================================================================== */

/**
 * Add the correct display in IE 10+.
 */

template {
  display: none;
}

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

[hidden] {
  display: none;
}

官方的注释很到位吧，欢迎在评论区交流。

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css 重置样式表（Normalize.css）