Using Fira Code for operators only in Atom

styles.less

atom-workspace {
  font-family: "Helvetica Neue";
}

atom-panel.tool-panel {
  //  font-size: 0.95em;
}

atom-text-editor.editor {
  font-size: 16px;
  font-weight: normal;
  line-height: 1.7;

  .syntax--entity.syntax--other.syntax--attribute-name.syntax--jsx,
  .syntax--storage.syntax--type.syntax--function.syntax--js,
  .syntax--storage.syntax--type.syntax--class.syntax--js {
      font-style: italic !important;
  }

  .syntax--keyword.syntax--operator,
  .syntax--storage.syntax--type.syntax--function.syntax--arrow.syntax--js {
    font-family: 'Fira Code';
    font-style: normal !important;
    text-rendering: optimizeLegibility;
  }
}

atom-text-editor .cursor-line .syntax--keyword.syntax--operator {
  text-rendering: auto;
}