This `.css` file is exactly the same as github's markdown css. In fact it was cut out from github website. I use it for my own github pages based blog: http://www.thomaszhao.cn/ 2015-01-15

github_markdown.css

/*! normalize.css v3.0.1 | MIT License | git.io/normalize */
/* It is cut out from `https://assets-cdn.github.com/assets/github-07ee5f9b28252daadba7750d43951602b35cdaa9dc19b5aff2eececebd6b6627.css`.
 * I use it for my own github pages based wiki: http://www.thomaszhao.cn/
 * Thomas, 2015-01-15 */
.markdown-body{
  overflow:hidden;
  font-family:"Helvetica Neue", Helvetica, "Segoe UI", Arial, freesans, sans-serif;
  font-size:16px;
  line-height:1.6;
  word-wrap:break-word
}

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

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

.markdown-body .absent{
  color:#c00
}

.markdown-body .anchor{
  position:absolute;
  top:0;
  bottom:0;
  left:0;
  display:block;
  padding-right:6px;
  padding-left:30px;
  margin-left:-30px
}

.markdown-body .anchor:focus{
  outline:none
}

.markdown-body h1,.markdown-body h2,.markdown-body h3,.markdown-body h4,.markdown-body h5,.markdown-body h6{
  position:relative;
  margin-top:1em;
  margin-bottom:16px;
  font-weight:bold;
  line-height:1.4
}

.markdown-body h1 .octicon-link,.markdown-body h2 .octicon-link,.markdown-body h3 .octicon-link,.markdown-body h4 .octicon-link,.markdown-body h5 .octicon-link,.markdown-body h6 .octicon-link{
  display:none;
  color:#000;
  vertical-align:middle
}

.markdown-body h1:hover .anchor,.markdown-body h2:hover .anchor,.markdown-body h3:hover .anchor,.markdown-body h4:hover .anchor,.markdown-body h5:hover .anchor,.markdown-body h6:hover .anchor{
  padding-left:8px;
  margin-left:-30px;
  line-height:1;
  text-decoration:none
}

.markdown-body h1:hover .anchor .octicon-link,.markdown-body h2:hover .anchor .octicon-link,.markdown-body h3:hover .anchor .octicon-link,.markdown-body h4:hover .anchor .octicon-link,.markdown-body h5:hover .anchor .octicon-link,.markdown-body h6:hover .anchor .octicon-link{
  display:inline-block
}

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

.markdown-body h1{
  padding-bottom:0.3em;
  font-size:2.25em;
  line-height:1.2;
  border-bottom:1px solid #eee
}

.markdown-body h2{
  padding-bottom:0.3em;
  font-size:1.75em;
  line-height:1.225;
  border-bottom:1px solid #eee
}

.markdown-body h3{
  font-size:1.5em;
  line-height:1.43
}

.markdown-body h4{
  font-size:1.25em
}

.markdown-body h5{
  font-size:1em
}

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

.markdown-body p,.markdown-body blockquote,.markdown-body ul,.markdown-body ol,.markdown-body dl,.markdown-body table,.markdown-body pre{
  margin-top:0;
  margin-bottom:16px
}

.markdown-body hr{
  height:4px;
  padding:0;
  margin:16px 0;
  background-color:#e7e7e7;
  border:0 none
}

.markdown-body ul,.markdown-body ol{
  padding-left:2em
}

.markdown-body ul.no-list,.markdown-body ol.no-list{
  padding:0;
  list-style-type:none
}

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

.markdown-body li>p{
  margin-top:16px
}

.markdown-body dl{
  padding:0
}

.markdown-body dl dt{
  padding:0;
  margin-top:16px;
  font-size:1em;
  font-style:italic;
  font-weight:bold
}

.markdown-body dl dd{
  padding:0 16px;
  margin-bottom:16px
}

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

.markdown-body blockquote>:first-child{
  margin-top:0
}

.markdown-body blockquote>:last-child{
  margin-bottom:0
}

.markdown-body table{
  display:block;
  width:100%;
  overflow:auto;
  word-break:normal;
  word-break:keep-all
}

.markdown-body table th{
  font-weight:bold
}

.markdown-body table th,.markdown-body table td{
  padding:6px 13px;
  border:1px solid #ddd
}

.markdown-body table tr{
  background-color:#fff;
  border-top:1px solid #ccc
}

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

.markdown-body img{
  max-width:100%;
  -moz-box-sizing:border-box;
  box-sizing:border-box
}

.markdown-body span.frame{
  display:block;
  overflow:hidden
}

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

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

.markdown-body span.frame span span{
  display:block;
  padding:5px 0 0;
  clear:both;
  color:#333
}

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

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

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

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

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

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

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

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

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

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

.markdown-body code,.markdown-body tt{
  padding:0;
  padding-top:0.2em;
  padding-bottom:0.2em;
  margin:0;
  font-size:85%;
  background-color:rgba(0,0,0,0.04);
  border-radius:3px
}

.markdown-body code:before,.markdown-body code:after,.markdown-body tt:before,.markdown-body tt:after{
  letter-spacing:-0.2em;
  content:"\00a0"
}

.markdown-body code br,.markdown-body tt br{
  display:none
}

.markdown-body del code{
  text-decoration:inherit
}

.markdown-body pre>code{
  padding:0;
  margin:0;
  font-size:100%;
  word-break:normal;
  white-space:pre;
  background:transparent;
  border:0
}

.markdown-body .highlight{
  margin-bottom:16px
}

.markdown-body .highlight pre,.markdown-body pre{
  padding:16px;
  overflow:auto;
  font-size:85%;
  line-height:1.45;
  background-color:#f7f7f7;
  border-radius:3px
}

.markdown-body .highlight pre{
  margin-bottom:0;
  word-break:normal
}

.markdown-body pre{
  word-wrap:normal
}

.markdown-body pre code,.markdown-body pre tt{
  display:inline;
  max-width:initial;
  padding:0;
  margin:0;
  overflow:initial;
  line-height:inherit;
  word-wrap:normal;
  background-color:transparent;
  border:0
}

.markdown-body pre code:before,.markdown-body pre code:after,.markdown-body pre tt:before,.markdown-body pre tt:after{
  content:normal
}

.markdown-body .csv-data td,.markdown-body .csv-data th{
  padding:5px;
  overflow:hidden;
  font-size:12px;
  line-height:1;
  text-align:left;
  white-space:nowrap
}

.markdown-body .csv-data .blob-num{
  padding:10px 8px 9px;
  text-align:right;
  background:#fff;
  border:0
}

.markdown-body .csv-data tr{
  border-top:0
}

.markdown-body .csv-data th{
  font-weight:bold;
  background:#f8f8f8;
  border-top:0
}