Subtle italics in Atom syntaxes

styles.less

atom-text-editor.editor {
    .syntax--punctuation.syntax--whitespace.syntax--comment.syntax--leading,
    .syntax--source {
        font-family: FiraCode-Retina; // https://github.com/tonsky/FiraCode
        text-rendering: optimizeLegibility;
        letter-spacing: 0;
    }

    .syntax--string.quoted,
    .syntax--string.regexp {
        -webkit-font-feature-settings: 'liga' off, 'calt' off;
    }

    .syntax--source.syntax--js.syntax--jsx > .keyword.control.flow.jsx,
    .syntax--comment, .syntax--type .syntax--function,
    // .syntax--storage.syntax--type:not(.syntax-arrow), // allow "Fira Code" to show arrow ligature,
    .syntax--constant.syntax--other.syntax--object.syntax--key,
    .syntax--entity.syntax--other.syntax--attribute-name.syntax--jsx,
    .syntax--keyword.syntax--control.syntax--flow,
    .syntax--keyword.syntax--control.syntax--module,
    .syntax--storage.syntax--modifier {
        // --- font variations:
        // Space Mono:
        // https://fonts.google.com/specimen/Space+Mono
        font-family: 'Space Mono';
        letter-spacing: -0.01em; // make "Space Mono" match "Fira Code" char width
        // --- or
        // Fantasque Sans Mono:
        // https://github.com/ryanoasis/nerd-fonts/tree/master/patched-fonts/FantasqueSansMono/Italic
        // font-family: FantasqueSansMonoNerdFontCM-Italic;
        // letter-spacing: 0.0825em; // make "Fantasque Sans Mono" match "Fira Code" char width
        // ---

        font-size: 1em;
        font-style: italic;
    }
}

Thank you!

BTW Line 16 should have :not(.syntax--arrow) in it.