In Atom 1.1, font features like ligatures finally work!

atom-custom-styles.less

atom-text-editor {
  // -> === /= => >>>
  -webkit-font-feature-settings: "liga" on, "calt" on;
  //-webkit-font-smoothing: antialiased;
  // text-rendering: optimizeLegibility;

  &::shadow {
    .meta.brace,
    .punctuation.terminator {
      opacity: 0.4;
      font-weight: 200;
    }

    .comment.documentation {
      color: #f8f8f8; // seti monokai's text color
    }
  }
}

atom-text-editor::shadow {
  .cursor-line {
    -webkit-font-feature-settings: "liga" off, "calt" off;
    // text-rendering: auto;
  }
}