给 MathJax 加上 Github 风格语法高亮

.markdown-body p > span.math {
  display: inline-block;
  font-size: 85%;
  padding: 2px 4px;
  border-radius: 3px;
  color: #24292e;
  background-color: #f6f8fa;
}
.markdown-body .math .mo {
  color: #d73a49;
}
.markdown-body .math .mn {
  color: #005cc5;
}