更正<sup>&<sub>行高
在Normalize.css,是相对位置真的有必要对<sup>与<sub>固定行高的问题？
/**
* Prevent `sub` and `sup` affecting `line-height` in all browsers.
*/
sub,
sup {
font-size: 75%;
line-height: 0;
position: relative;
vertical-align: baseline;
}
sup {
top: -0.5em;
}
sub {
bottom: -0.25em;
}
使用浏览器默认值有vertical-align: sup/sub什么问题？
或者换句话说,为什么不简单地声明sub, sup { line-height: 0; }呢？
让我们看看normalize.css 背后的想法。来自normalize.css Github 页面：
\n\n\nNormalize.css 使浏览器更一致地渲染所有元素并符合现代标准。它精确地仅针对需要规范化的\n样式。
\n
该声明的主要关键词是“一致”。
\n在这些屏幕截图中，顶行有line-height: 0和font-size: 75%代表 sub 和 super。底线具有规范化的 CSS，并且在浏览器之间的位置更加一致。
IE6
\n
IE8
\n
IE11
\n
Chrome \xe2\x80\x94 在现代浏览器中差异并不那么大。
\n
差异很小，但标准化 CSS 可以在浏览器（包括 IE6）之间提供更一致的外观。这种一致性是通过使用实现的position: relative。
这就是我用于屏幕截图的内容
\n也作为jsBin 的例子。将 jsbin 链接插入netrenderer.com后截取的 IE 屏幕截图
\n\r\n
\r\n\n
\r\n
\r\nbody {\n background: #CCC;\n}\n\np {\n background: #F00;\n}\n\n\n\n\n\n\n\n\n\n/*! normalize.css v3.0.2 | MIT License | git.io/normalize */\n\n/**\n * 1. Set default font family to sans-serif.\n * 2. Prevent iOS text size adjust after orientation change, without disabling\n * user zoom.\n */\n\nhtml {\n font-family: sans-serif; /* 1 */\n -ms-text-size-adjust: 100%; /* 2 */\n -webkit-text-size-adjust: 100%; /* 2 */\n}\n\n/**\n * Remove default margin.\n */\n\nbody {\n margin: 0;\n}\n\n/* HTML5 display definitions\n ========================================================================== */\n\n/**\n * Correct `block` display not defined for any HTML5 element in IE 8/9.\n * Correct `block` display not defined for `details` or `summary` in IE 10/11\n * and Firefox.\n * Correct `block` display not defined for `main` in IE 11.\n */\n\narticle,\naside,\ndetails,\nfigcaption,\nfigure,\nfooter,\nheader,\nhgroup,\nmain,\nmenu,\nnav,\nsection,\nsummary {\n display: block;\n}\n\n/**\n * 1. Correct `inline-block` display not defined in IE 8/9.\n * 2. Normalize vertical alignment of `progress` in Chrome, Firefox, and Opera.\n */\n\naudio,\ncanvas,\nprogress,\nvideo {\n display: inline-block; /* 1 */\n vertical-align: baseline; /* 2 */\n}\n\n/**\n * Prevent modern browsers from displaying `audio` without controls.\n * Remove excess height in iOS 5 devices.\n */\n\naudio:not([controls]) {\n display: none;\n height: 0;\n}\n\n/**\n * Address `[hidden]` styling not present in IE 8/9/10.\n * Hide the `template` element in IE 8/9/11, Safari, and Firefox < 22.\n */\n\n[hidden],\ntemplate {\n display: none;\n}\n\n/* Links\n ========================================================================== */\n\n/**\n * Remove the gray background color from active links in IE 10.\n */\n\na {\n background-color: transparent;\n}\n\n/**\n * Improve readability when focused and also mouse hovered in all browsers.\n */\n\na:active,\na:hover {\n outline: 0;\n}\n\n/* Text-level semantics\n ========================================================================== */\n\n/**\n * Address styling not present in IE 8/9/10/11, Safari, and Chrome.\n */\n\nabbr[title] {\n border-bottom: 1px dotted;\n}\n\n/**\n * Address style set to `bolder` in Firefox 4+, Safari, and Chrome.\n */\n\nb,\nstrong {\n font-weight: bold;\n}\n\n/**\n * Address styling not present in Safari and Chrome.\n */\n\ndfn {\n font-style: italic;\n}\n\n/**\n * Address variable `h1` font-size and margin within `section` and `article`\n * contexts in Firefox 4+, Safari, and Chrome.\n */\n\nh1 {\n font-size: 2em;\n margin: 0.67em 0;\n}\n\n/**\n * Address styling not present in IE 8/9.\n */\n\nmark {\n background: #ff0;\n color: #000;\n}\n\n/**\n * Address inconsistent and variable font size in all browsers.\n */\n\nsmall {\n font-size: 80%;\n}\n\n\n\n/* Embedded content\n ========================================================================== */\n\n/**\n * Remove border when inside `a` element in IE 8/9/10.\n */\n\nimg {\n border: 0;\n}\n\n/**\n * Correct overflow not hidden in IE 9/10/11.\n */\n\nsvg:not(:root) {\n overflow: hidden;\n}\n\n/* Grouping content\n ========================================================================== */\n\n/**\n * Address margin not present in IE 8/9 and Safari.\n */\n\nfigure {\n margin: 1em 40px;\n}\n\n/**\n * Address differences between Firefox and other browsers.\n */\n\nhr {\n -moz-box-sizing: content-box;\n box-sizing: content-box;\n height: 0;\n}\n\n/**\n * Contain overflow in all browsers.\n */\n\npre {\n overflow: auto;\n}\n\n/**\n * Address odd `em`-unit font size rendering in all browsers.\n */\n\ncode,\nkbd,\npre,\nsamp {\n font-family: monospace, monospace;\n font-size: 1em;\n}\n\n/* Forms\n ========================================================================== */\n\n/**\n * Known limitation: by default, Chrome and Safari on OS X allow very limited\n * styling of `select`, unless a `border` property is set.\n */\n\n/**\n * 1. Correct color not being inherited.\n * Known issue: affects color of disabled elements.\n * 2. Correct font properties not being inherited.\n * 3. Address margins set differently in Firefox 4+, Safari, and Chrome.\n */\n\nbutton,\ninput,\noptgroup,\nselect,\ntextarea {\n color: inherit; /* 1 */\n font: inherit; /* 2 */\n margin: 0; /* 3 */\n}\n\n/**\n * Address `overflow` set to `hidden` in IE 8/9/10/11.\n */\n\nbutton {\n overflow: visible;\n}\n\n/**\n * Address inconsistent `text-transform` inheritance for `button` and `select`.\n * All other form control elements do not inherit `text-transform` values.\n * Correct `button` style inheritance in Firefox, IE 8/9/10/11, and Opera.\n * Correct `select` style inheritance in Firefox.\n */\n\nbutton,\nselect {\n text-transform: none;\n}\n\n/**\n * 1. Avoid the WebKit bug in Android 4.0.* where (2) destroys native `audio`\n * and `video` controls.\n * 2. Correct inability to style clickable `input` types in iOS.\n * 3. Improve usability and consistency of cursor style between image-type\n * `input` and others.\n */\n\nbutton,\nhtml input[type="button"], /* 1 */\ninput[type="reset"],\ninput[type="submit"] {\n -webkit-appearance: button; /* 2 */\n cursor: pointer; /* 3 */\n}\n\n/**\n * Re-set default cursor for disabled elements.\n */\n\nbutton[disabled],\nhtml input[disabled] {\n cursor: default;\n}\n\n/**\n * Remove inner padding and border in Firefox 4+.\n */\n\nbutton::-moz-focus-inner,\ninput::-moz-focus-inner {\n border: 0;\n padding: 0;\n}\n\n/**\n * Address Firefox 4+ setting `line-height` on `input` using `!important` in\n * the UA stylesheet.\n */\n\ninput {\n line-height: normal;\n}\n\n/**\n * It\'s recommended that you don\'t attempt to style these elements.\n * Firefox\'s implementation doesn\'t respect box-sizing, padding, or width.\n *\n * 1. Address box sizing set to `content-box` in IE 8/9/10.\n * 2. Remove excess padding in IE 8/9/10.\n */\n\ninput[type="checkbox"],\ninput[type="radio"] {\n box-sizing: border-box; /* 1 */\n padding: 0; /* 2 */\n}\n\n/**\n * Fix the cursor style for Chrome\'s increment/decrement buttons. For certain\n * `font-size` values of the `input`, it causes the cursor style of the\n * decrement button to change from `default` to `text`.\n */\n\ninput[type="number"]::-webkit-inner-spin-button,\ninput[type="number"]::-webkit-outer-spin-button {\n height: auto;\n}\n\n/**\n * 1. Address `appearance` set to `searchfield` in Safari and Chrome.\n * 2. Address `box-sizing` set to `border-box` in Safari and Chrome\n * (include `-moz` to future-proof).\n */\n\ninput[type="search"] {\n -webkit-appearance: textfield; /* 1 */\n -moz-box-sizing: content-box;\n -webkit-box-sizing: content-box; /* 2 */\n box-sizing: content-box;\n}\n\n/**\n * Remove inner padding and search cancel button in Safari and Chrome on OS X.\n * Safari (but not Chrome) clips the cancel button when the search input has\n * padding (and `textfield` appearance).\n */\n\ninput[type="search"]::-webkit-search-cancel-button,\ninput[type="search"]::-webkit-search-decoration {\n -webkit-appearance: none;\n}\n\n/**\n * Define consistent border, margin, and padding.\n */\n\nfieldset {\n border: 1px solid #c0c0c0;\n margin: 0 2px;\n padding: 0.35em 0.625em 0.75em;\n}\n\n/**\n * 1. Correct `color` not being inherited in IE 8/9/10/11.\n * 2. Remove padding so people aren\'t caught out if they zero out fieldsets.\n */\n\nlegend {\n border: 0; /* 1 */\n padding: 0; /* 2 */\n}\n\n/**\n * Remove default vertical scrollbar in IE 8/9/10/11.\n */\n\ntextarea {\n overflow: auto;\n}\n\n/**\n * Don\'t inherit the `font-weight` (applied by a rule above).\n * NOTE: the default cannot safely be changed in Chrome and Safari on OS X.\n */\n\noptgroup {\n font-weight: bold;\n}\n\n/* Tables\n ========================================================================== */\n\n/**\n * Remove most spacing between table cells.\n */\n\ntable {\n border-collapse: collapse;\n border-spacing: 0;\n}\n\ntd,\nth {\n padding: 0;\n}\n\n\n.line0 sub, .line0 sup { line-height: 0; font-size: 75%;}\n\n.normalize sub,\n.normalize sup {\n font-size: 75%;\n line-height: 0;\n position: relative;\n vertical-align: baseline;\n}\n\n.normalize sup {\n top: -0.5em;\n}\n\n.normalize sub {\n bottom: -0.25em;\n}<p class="line0">Hello <sub>there,</sub> How<sup>are you?</sup>\n</p>\n\n<p class="normalize">Hello <sub>there,</sub> How<sup>are you?</sup>\n</p>