It matches any single element in the document tree. A type selector matches every instance of the element type in the document tree.
Descendant selectors express such a relationship in a pattern.
A descendant selector is made up of two or more selectors separed by whitespace. A child selector matches when an element is the child of some element. The selector matches if E1 and E2 share the same parent in the tree and E1 immediately precedes E2. If the selector is used, the words in the value must not contains spaces. The match always starts at the beginning of the attribute value.