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Element lists are separated by a comma.
notes, topic {display:block}

Context is separated by space
notes topic {color:red} meaning the color red will affect “topic” only when the “topic” is in the tag “notes”

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in xml file:

the author is not defined in the css as a content nor selector but a attribute.
It can be added to the document as generated content.
slide:after{content:” Responsible:” attr(author);
display:block; font-style:italic;
}