My Atom Stylesheet (add support for language-markdown)

styles.less

// Fix Material Theme with language-markdown
@font-face {
    font-family: AdobeOpenSourceFont-Latin;
    src: local(SourceCodePro-Light);
}

@font-face {
    font-family: AdobeOpenSourceFont-Latin;
    font-style: italic;
    src: local(SourceCodePro-LightIt);
}

@font-face {
    font-family: AdobeOpenSourceFont-Latin;
    font-weight: 500;
    src: local(SourceCodePro-Semibold);
}

@font-face {
    font-family: AdobeOpenSourceFont-Latin;
    font-style: italic;
    font-weight: 500;
    src: local(SourceCodePro-SemiboldIt);
}

@font-face {
    font-family: AdobeOpenSourceFont-CJK;
    src: local(SourceHanSansTC-Light);
}

@font-face {
    font-family: AdobeOpenSourceFont-CJK;
    font-weight: 500;
    src: local(SourceHanSansTC-Medium);
}

atom-text-editor {
    font-family: AdobeOpenSourceFont-Latin, AdobeOpenSourceFont-CJK !important;
}

atom-text-editor {
  .syntax--heading.syntax--markup.syntax--md {
    .syntax--heading-1 {
      color: #4FC3F7;
    }
    .syntax--heading-2 {
      color: #29B6F6;
    }
    .syntax--heading-3 {
      color: #03A9F4;
    }
    .syntax--heading-4 {
      color: #039BE5;
    }
    .syntax--heading-5 {
      color: #0288D1;
    }
    .syntax--heading-6 {
      color: #0277BD;
    }
  }
  .syntax--link.syntax--markup.syntax--md {
    .syntax--string {
      color: #C3E88D;

      .syntax--punctuation.syntax--md {
        color: #C3E88D;
      }
    }
    .syntax--punctuation.syntax--md, .syntax--destination.syntax--link.syntax--md {
      color: #757575;
    }
  }
  .syntax--code.syntax--raw.syntax--markup.syntax--md {
    color: #eeeeee;
    background-color: #424242;
  }
  .syntax--hr.syntax--md {
    color: #607d8b;
  }
}