1. A method of managing cascading style sheet rules, comprising: identifying, by a web application on a server, a markup page of content items; designating, by the web application, a plurality of super-themes by: defining a first markup element that associates a first container that contains a first content item of the markup page and a first cascading style sheet rule, with a first cascading style sheet class; designating the first markup element by a first super-theme; defining a second markup element that associates a second container that contains a second content item of the markup page and a second cascading style sheet rule, with a second cascading style sheet class different from the first cascading style sheet class; and designating the second markup element by a second super-theme; loading a common cascading style sheet for the markup page; automatically modifying, by a processor, the common cascading style sheet to use the first super-theme as a parent selector for selecting the first cascading style sheet rule from the first container, which is applied to the first content item, wherein: the first super-theme causes the first cascading style sheet rule to apply only to the first content item, such that the first cascading style sheet rule does not override other cascading style sheet rules; and automatically modifying, by the processor, the common cascading style sheet to use the second super-theme as a parent selector for selecting the second cascading style sheet rule from the second set of cascading style sheet rules, which is applied to the second content item, wherein: the second super-theme causes the second cascading style sheet rule to apply only to the second content item, such that the second cascading style sheet rule does not override other cascading style sheet rules.