If there is no active app, then it calls start_app().
Value
A list of data frames with the active themes. Each data frame row is a style that applies to selected CLI tree nodes. Each data frame has columns:
selector: The original CSS-like selector string. See themes.parsed: The parsed selector, as used by cli for matching to nodes.style: The original style.cnt: The id of the container the style is currently applied to, orNAif the style is not used.