Operator Mono + FiraCode ligatures in Atom

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atom-text-editor {
   font-family: "Operator Mono";
   font-size: 14px;
   font-weight: 400;
   line-height: 1.7;
}

.entity.other.attribute-name,
.entity.name.function {
    font-style: italic;
}
atom-text-editor::shadow {
    text-rendering: optimizeLegibility;

    .entity.other.attribute-name,
    .storage.type.function.js,
    .storage.type.class.js {
        font-family: 'Operator Mono';
        font-style: italic;
    }

    .keyword.operator,
    .storage.type.function.arrow.js {
      font-family: 'Fira Code';
    }
}

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