about

body > p#one {color:red;}

This text will be red if the rule has been applied.

html > p#two {color:red;}

This text will be red if the rule has been applied.

html>body p#three {color:red;}

This text will be red if the rule has been applied.

html > body p#four {color:red;}

This text will be red if the rule has been applied.