重置样式非常多，凡是一个前端开发人员肯定有一个常用的重置CSS文件并知道如何使用它们。他们是盲目的在做还是知道为什么这么做呢？原因是不同的浏览器对一些元素有不同的默认样式，如果你不处理，在不同的浏览器下会存在必要的风险，或者更有戏剧性的性发生。 

* {      padding: 0;      margin: 0;}

　　这是最普遍最简单的CSS重设，将所有元素的padding和margin值都设为0，可以避免一些浏览器在理解这两个属性默认值上的”分歧”。

/*! 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,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 */}

　　normalize.css没有重置所有的样式风格，但仅提供了一套合理的默认样式值。既能让众多浏览器达到一致和合理，但又不扰乱其他的东西（如粗体的标题）。

　　一种清除,一种保留兼容