GitHub Markdown CSS Clone (should look exactly the same).

GitHub2 Clone.css

/*
Trying to rewrite the original GitHub Markdown CSS
Last Update 14-01-08 by Luis Gerhorst
*/

body {
	font-family: Helvetica, sans-serif;
	font-size: 15px;
	line-height: 1.7;
	background-color: white;
	padding: 30px;
}

body > *:first-child {
	margin-top: 0 !important;
}

body > *:last-child {
	margin-bottom: 0 !important;
}

a {
	color: #4183c4;
	/* can not remove underline */
}

em {
	font-family: "Helvetica Neue", sans-serif; /* for better contrast to normal text */
}

a.absent {
	color: #cc0000;
}

a.anchor {
	display: block;
	padding-left: 30px;
	margin-left: -30px;
	cursor: pointer;
	position: absolute;
	top: 0;
	left: 0;
	bottom: 0;
}

h1, h2, h3, h4, h5, h6 {
	margin: 1em 0 15px;
	padding: 0;
	font-weight: bold;
	-webkit-font-smoothing: antialiased;
	cursor: text;
	position: relative;
}

h1:hover a.anchor, h2:hover a.anchor, h3:hover a.anchor, h4:hover a.anchor, h5:hover a.anchor, h6:hover a.anchor {
	background: url(data:image/png;base64,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) no-repeat 10px center;
	text-decoration: none;
}

h1 tt, h1 code, h2 tt, h2 code, h3 tt, h3 code, h4 tt, h4 code, h5 tt, h5 code, h6 tt, h6 code {
	font-size: inherit;
}

h1 {
	font-size: 2.5em;
	border-bottom: 1px solid #ddd;
	color: black;
}

h2 {
	font-size: 2em;
	border-bottom: 1px solid #eee;
	color: black;
}

h3 {
	font-size: 1.5em;
}

h4 {
	font-size: 1.2em;
}

h5 {
	font-size: 1em;
}

h6 {
	color: #777;
	font-size: 1em;
}

p, blockquote, ul, ol, dl, li, table, pre {
	margin: 15px 0;
}

ul ul, ul ol, ol ol, ol ul {
	margin-top: 0;
	margin-bottom: 0;
}

hr {
	background: transparent url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAYAAAAECAYAAACtBE5DAAAAGXRFWHRTb2Z0d2FyZQBBZG9iZSBJbWFnZVJlYWR5ccllPAAAAyJpVFh0WE1MOmNvbS5hZG9iZS54bXAAAAAAADw/eHBhY2tldCBiZWdpbj0i77u/IiBpZD0iVzVNME1wQ2VoaUh6cmVTek5UY3prYzlkIj8+IDx4OnhtcG1ldGEgeG1sbnM6eD0iYWRvYmU6bnM6bWV0YS8iIHg6eG1wdGs9IkFkb2JlIFhNUCBDb3JlIDUuMC1jMDYwIDYxLjEzNDc3NywgMjAxMC8wMi8xMi0xNzozMjowMCAgICAgICAgIj4gPHJkZjpSREYgeG1sbnM6cmRmPSJodHRwOi8vd3d3LnczLm9yZy8xOTk5LzAyLzIyLXJkZi1zeW50YXgtbnMjIj4gPHJkZjpEZXNjcmlwdGlvbiByZGY6YWJvdXQ9IiIgeG1sbnM6eG1wPSJodHRwOi8vbnMuYWRvYmUuY29tL3hhcC8xLjAvIiB4bWxuczp4bXBNTT0iaHR0cDovL25zLmFkb2JlLmNvbS94YXAvMS4wL21tLyIgeG1sbnM6c3RSZWY9Imh0dHA6Ly9ucy5hZG9iZS5jb20veGFwLzEuMC9zVHlwZS9SZXNvdXJjZVJlZiMiIHhtcDpDcmVhdG9yVG9vbD0iQWRvYmUgUGhvdG9zaG9wIENTNSBNYWNpbnRvc2giIHhtcE1NOkluc3RhbmNlSUQ9InhtcC5paWQ6OENDRjNBN0E2NTZBMTFFMEI3QjRBODM4NzJDMjlGNDgiIHhtcE1NOkRvY3VtZW50SUQ9InhtcC5kaWQ6OENDRjNBN0I2NTZBMTFFMEI3QjRBODM4NzJDMjlGNDgiPiA8eG1wTU06RGVyaXZlZEZyb20gc3RSZWY6aW5zdGFuY2VJRD0ieG1wLmlpZDo4Q0NGM0E3ODY1NkExMUUwQjdCNEE4Mzg3MkMyOUY0OCIgc3RSZWY6ZG9jdW1lbnRJRD0ieG1wLmRpZDo4Q0NGM0E3OTY1NkExMUUwQjdCNEE4Mzg3MkMyOUY0OCIvPiA8L3JkZjpEZXNjcmlwdGlvbj4gPC9yZGY6UkRGPiA8L3g6eG1wbWV0YT4gPD94cGFja2V0IGVuZD0iciI/PqqezsUAAAAfSURBVHjaYmRABcYwBiM2QSA4y4hNEKYDQxAEAAIMAHNGAzhkPOlYAAAAAElFTkSuQmCC) repeat-x 0 0;
	border: 0 none;
	color: #ddd;
	height: 4px;
	padding: 0;
}

body > h2:first-child {
	margin-top: 0;
	padding-top: 0;
}

body > h1:first-child {
	margin-top: 0;
	padding-top: 0;
}

body > h1:first-child + h2 {
	margin-top: 0;
	padding-top: 0;
}

body > h3:first-child, body > h4:first-child, body > h5:first-child, body > h6:first-child {
	margin-top: 0;
	padding-top: 0;
}

a:first-child h1, a:first-child h2, a:first-child h3, a:first-child h4, a:first-child h5, a:first-child h6 {
	margin-top: 0;
	padding-top: 0;
}

h1 p, h2 p, h3 p, h4 p, h5 p, h6 p {
	margin-top: 0;
}

li p.first {
	display: inline-block;
}

li {
	margin: 0;
}

ul, ol {
	padding-left: 30px;
}

ul :first-child, ol :first-child {
	margin-top: 0;
}

dl {
	padding: 0;
}

dl dt {
	font-size: 14px;
	font-weight: bold;
	font-style: italic;
	padding: 0;
	margin: 15px 0 5px;
}

dl dt:first-child {
	padding: 0;
}

dl dt > :first-child {
	margin-top: 0;
}

dl dt > :last-child {
	margin-bottom: 0;
}

dl dd {
	margin: 0 0 15px;
	padding: 0 15px;
}

dl dd > :first-child {
	margin-top: 0;
}

dl dd > :last-child {
	margin-bottom: 0;
}

blockquote {
	border-left: 4px solid #ddd;
	padding: 0 15px;
	color: #777;
}

blockquote > :first-child {
	margin-top: 0;
}

blockquote > :last-child {
	margin-bottom: 0;
}

table {
	padding: 0;
	border-collapse: collapse;
}

table tr {
	border-top: 1px solid #ddd;
	background-color: white;
	margin: 0;
	padding: 0;
}

table tr:nth-child(2n) {
	background-color: #f8f8f8;
}

table tr th {
	font-weight: bold;
	border: 1px solid #ddd;
	margin: 0;
	padding: 6px 13px;
}

table tr td {
	border: 1px solid #ddd;
	margin: 0;
	padding: 6px 13px;
}

table tr th :first-child, table tr td :first-child {
	margin-top: 0;
}

table tr th :last-child, table tr td :last-child {
	margin-bottom: 0;
}

img {
	max-width: 100%;
	height: auto;
}

span.frame {
	display: block;
	overflow: hidden;
}

span.frame > span {
	border: 1px solid #ddd;
	display: block;
	float: left;
	overflow: hidden;
	margin: 13px 0 0;
	padding: 7px;
	width: auto;
}

span.frame span img {
	display: block;
	float: left;
}

span.frame span span {
	clear: both;
	color: #333333;
	display: block;
	padding: 5px 0 0;
}

span.align-center {
	display: block;
	overflow: hidden;
	clear: both;
}

span.align-center > span {
	display: block;
	overflow: hidden;
	margin: 13px auto 0;
	text-align: center;
}

span.align-center span img {
	margin: 0 auto;
	text-align: center;
}

span.align-right {
	display: block;
	overflow: hidden;
	clear: both;
}

span.align-right > span {
	display: block;
	overflow: hidden;
	margin: 13px 0 0;
	text-align: right;
}

span.align-right span img {
	margin: 0;
	text-align: right;
}

span.float-left {
	display: block;
	margin-right: 13px;
	overflow: hidden;
	float: left;
}

span.float-left span {
	margin: 13px 0 0;
}

span.float-right {
	display: block;
	margin-left: 13px;
	overflow: hidden;
	float: right;
}

span.float-right > span {
	display: block;
	overflow: hidden;
	margin: 13px auto 0;
	text-align: right;
}

code, tt {
	font: 12px Consolas, "Liberation Mono", Courier, monospace;
	margin: 0 2px;
	padding: 0 5px;
	white-space: nowrap;
	border: 1px solid #ddd;
	background-color: #f8f8f8;
	border-radius: 3px;
}

pre code {
	margin: 0;
	padding: 0;
	white-space: pre;
	border: none;
	background: transparent;
}

pre {
	background-color: #f8f8f8;
	border: 1px solid #ddd;
	font-size: 13px;
	line-height: 19px;
	overflow: auto;
	padding: 6px 10px;
	border-radius: 3px;
	word-wrap: normal;
}

pre code, pre tt {
	background-color: transparent;
	border: none;
}

sup {
	font-size: 0.83em;
	vertical-align: super;
	line-height: 0;
}

* {
	-webkit-print-color-adjust: exact;
}

@media screen and (min-width: 914px) {
	body {
		width: 854px;
		margin: 0 auto;
	};
}

@media print {
	table, pre {
		page-break-inside: avoid;
	}

	pre {
		word-wrap: break-word;
	};
}

Trying to create a markdown CSS that exactly matches the one GitHub is using. If you find any errors feel free to fix them. Code is based one Mou for Mac's GitHub2 CSS from 14-01-08.