In Lux-Syntax\index.less:

Starting from Atom v1.13.0, the contents of atom-text-editor elements are no longer encapsulated within a shadow DOM boundary. This means you should stop using :host and ::shadow pseudo-selectors, and prepend all your syntax selectors with syntax--. To prevent breakage with existing style sheets, Atom will automatically upgrade the following selectors:

• atom-text-editor, :host => atom-text-editor,atom-text-editor

• atom-text-editor .gutter, :host .gutter => atom-text-editor .gutter,atom-text-editor .gutter

• atom-text-editor .gutter .line-number.cursor-line, :host .gutter .line-number.cursor-line => atom-text-editor .gutter .line-number.cursor-line,atom-text-editor .gutter .line-number.cursor-line

• atom-text-editor .gutter .line-number.cursor-line-no-selection, :host .gutter .line-number.cursor-line-no-selection => atom-text-editor .gutter .line-number.cursor-line-no-selection,atom-text-editor .gutter .line-number.cursor-line-no-selection

• atom-text-editor .wrap-guide, :host .wrap-guide => atom-text-editor .wrap-guide,atom-text-editor .wrap-guide

• atom-text-editor .indent-guide, :host .indent-guide => atom-text-editor .indent-guide,atom-text-editor .indent-guide

• atom-text-editor .invisible-character, :host .invisible-character => atom-text-editor .invisible-character,atom-text-editor .invisible-character

• atom-text-editor .search-results .marker .region, :host .search-results .marker .region => atom-text-editor .search-results .syntax--marker .region,atom-text-editor .search-results .syntax--marker .region

• atom-text-editor .search-results .marker.current-result .region, :host .search-results .marker.current-result .region => atom-text-editor .search-results .syntax--marker.current-result .region,atom-text-editor .search-results .syntax--marker.current-result .region

• atom-text-editor.is-focused .cursor, :host(.is-focused) .cursor => atom-text-editor.is-focused .cursor,atom-text-editor .cursor

• atom-text-editor.is-focused .selection .region, :host(.is-focused) .selection .region => atom-text-editor.is-focused .selection .region,atom-text-editor .selection .region

• atom-text-editor.is-focused .line-number.cursor-line-no-selection, atom-text-editor.is-focused .line.cursor-line, :host(.is-focused) .line-number.cursor-line-no-selection, :host(.is-focused) .line.cursor-line => atom-text-editor.is-focused .line-number.cursor-line-no-selection, atom-text-editor.is-focused .line.cursor-line,atom-text-editor .line-number.cursor-line-no-selection,atom-text-editor .line.cursor-line

• .comment => .syntax--comment

• .constant => .syntax--constant

• .entity => .syntax--entity

• .keyword => .syntax--keyword

• .storage => .syntax--storage

• .storage.type => .syntax--storage.syntax--type

• .string => .syntax--string

• .support => .syntax--support

• .entity.name.class, .entity.name.type.class, .support.type, .support.class => .syntax--entity.syntax--name.syntax--class, .syntax--entity.syntax--name.syntax--type.syntax--class, .syntax--support.syntax--type, .syntax--support.syntax--class

• .variable => .syntax--variable

• .invalid => .syntax--invalid

• .text .source => .syntax--text .syntax--source

• .text.html.ruby .source => .syntax--text.syntax--html.syntax--ruby .syntax--source

• `.entity.other.inherited-clas