If you are using a style that does not contain all of the html files and all of the css files just like prosilver, then it is a child of prosilver since it uses some of prosilver's files.
a style that contains all of its own files is not a child and you would do any edits to only the files contained in it.
if a style is a child of another style, then any edits you need to do to a file that is not contained in its folders has to be done to the other style.
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If a tree falls in the forest and nobody is there, does it make a sound?