A coderay theme that mimicks GitHub syntax highlighting (not perfect, still a work-in-progress, but close...)

coderay-github.css

/* https://gist.github.com/kellyredding/30ac3bbf4534e00b0c04 */

code,
.CodeRay,
.CodeRay * {
  box-sizing: border-box;
}

code,
.CodeRay .code pre {
  font-family: Consolas,"Liberation Mono",Menlo,Courier,monospace;
  color: #333;
}

.CodeRay .code pre {
  font-size: 13px;
  line-height: 19px;
  overflow: auto;
}

code,
.CodeRay {
  background-color: #f8f8f8;
  border: 1px solid #ddd;
  border-radius: 3px;
}

code {
  margin: 0;
  padding: 0;
}

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

.CodeRay {
  padding: 6px 10px;
  margin: 15px 0;
}

.CodeRay pre {
  margin: 0;
  padding: 0;
}

div.CodeRay { }
span.CodeRay { white-space: pre; border: 0px; padding: 2px }

table.CodeRay { border-collapse: collapse; width: 100%; padding: 2px }
table.CodeRay td {
  padding: 1em 0.5em;
  vertical-align: top;
}

.CodeRay .line-numbers, .CodeRay .no {
  background-color: #ECECEC;
  color: #AAA;
  text-align: right;
}

.CodeRay .line-numbers a {
  color: #AAA;
}

.CodeRay .line-numbers tt { font-weight: bold }
.CodeRay .line-numbers .highlighted { color: red }
.CodeRay .line { display: block; float: left; width: 100%; }
.CodeRay span.line-numbers { padding: 0px 4px }
.CodeRay .code { width: 100% }

ol.CodeRay { font-size: 10pt }
ol.CodeRay li { white-space: pre }

.CodeRay .debug { color:white ! important; background:blue ! important; }

.CodeRay .annotation { color:#007 }
.CodeRay .attribute-name { color:teal }
.CodeRay .attribute-value { color:#700 }
.CodeRay .binary { color:#509; font-weight:bold }
.CodeRay .comment  { color:#998; font-style: italic;}
.CodeRay .char { color:#04D }
.CodeRay .char .content { color:#04D }
.CodeRay .char .delimiter { color:#039 }
.CodeRay .class { color:#458; font-weight:bold }
.CodeRay .complex { color:#A08; font-weight:bold }
.CodeRay .constant { color:teal; }
.CodeRay .color { color:#0A0 }
.CodeRay .class-variable { color:#369 }
.CodeRay .decorator { color:#B0B; }
.CodeRay .definition { color:#099; font-weight:bold }
.CodeRay .directive { color:#088; font-weight:bold }
.CodeRay .delimiter { color:black }
.CodeRay .doc { color:#970 }
.CodeRay .doctype { color:#998; font-weight:bold }
.CodeRay .doc-string { color:#D42; font-weight:bold }
.CodeRay .escape  { color:#666; font-weight:bold }
.CodeRay .entity { color:#800; font-weight:bold }
.CodeRay .error { color:#F00; background-color:#FAA }
.CodeRay .exception { color:#C00; font-weight:bold }
.CodeRay .filename { color:#099; }
.CodeRay .function { color:#900; font-weight:bold }
.CodeRay .global-variable { color: #0086b3 }
.CodeRay .hex { color:#058; font-weight:bold }
.CodeRay .integer  { color:#099; }
.CodeRay .include { color:#B44; font-weight:bold }
.CodeRay .inline { color: black }
.CodeRay .inline .inline { background: #ccc }
.CodeRay .inline .inline .inline { background: #bbb }
.CodeRay .inline .inline-delimiter { color: #D14; }
.CodeRay .inline-delimiter { color: #D14; }
.CodeRay .important { color:#f00; }
.CodeRay .interpreted { color:#B2B; font-weight:bold }
.CodeRay .instance-variable { color:teal }
.CodeRay .label { color:#970; font-weight:bold }
.CodeRay .local-variable { color:#963 }
.CodeRay .octal { color:#40E; font-weight:bold }
.CodeRay .operator { }
.CodeRay .predefined-constant { color:teal; }
.CodeRay .predefined { color:#369; font-weight:bold }
.CodeRay .preprocessor { color:#579; }
.CodeRay .pseudo-class { color:#458; font-weight:bold }
.CodeRay .predefined-type { color:#074; font-weight:bold }
.CodeRay .reserved, .keyword  { color:#000; font-weight:bold }

.CodeRay .key { color: #808; }
.CodeRay .key .delimiter { color: #606; }
.CodeRay .key .char { color: #80f; }
.CodeRay .value { color: #088; }

.CodeRay .regexp { color: #009926 }
.CodeRay .regexp .char { color: #009926 }
.CodeRay .regexp .content { color: #009926 }
.CodeRay .regexp .delimiter { color: #009926 }
.CodeRay .regexp .modifier { color: #009926 }
.CodeRay .regexp .function  { color: #009926 }

.CodeRay .string { color: #D20; }
.CodeRay .string .string { }
.CodeRay .string .string .string { background-color:#ffd0d0 }
.CodeRay .string .content { color: #D14; }
.CodeRay .string .char { color: #D14; }
.CodeRay .string .delimiter { color: #D14; }

.CodeRay .shell { color:#D14 }
.CodeRay .shell .content { }
.CodeRay .shell .delimiter { color:#D14 }

.CodeRay .symbol { color:#990073 }
.CodeRay .symbol .content { color:#A60 }
.CodeRay .symbol .delimiter { color:#630 }

.CodeRay .tag { color:navy }
.CodeRay .tag-special { color:#D70; font-weight:bold }
.CodeRay .type { color:#339; font-weight:bold }
.CodeRay .variable  { color:#036 }

.CodeRay .insert { background: #afa; }
.CodeRay .delete { background: #faa; }
.CodeRay .change { color: #aaf; background: #007; }
.CodeRay .head { color: #f8f; background: #505 }

.CodeRay .insert .insert { color: #080; font-weight:bold }
.CodeRay .delete .delete { color: #800; font-weight:bold }
.CodeRay .change .change { color: #66f; }
.CodeRay .head .head { color: #f4f; }

(notes to self)

CSS and JSON is off a bit (due to limitations in coderay assigned classes):

• Coderay assigns just a generic "key" and "value" to both CSS and JSON key: value statements
• "key"s are set to #808 (purple) for both
• "value"s are set based on their type (string, etc) but it differs from how GitHub does it

All of this is just FYI.