1. A computer system comprising: one or more hardware computer processors, and one or more computer storage media coupled to the one or more hardware computer processors and having thereon computer-executable instructions that are structured such that, when executed by one or more processors of the computer system, cause the computer system to perform the following: evaluating an authored style rule set comprising one or more authored rules that are each defined to apply properties to markup language elements matching a markup language element type, to identify with respect to a markup language document having one or more markup language elements and markup language types, which of the defined properties affect how a specific markup language element of the markup language document is rendered when the authored rules are applied to the markup language document; deriving a derived style rule set of one or more style rules by defining for each of the one or more style rules, one or more of the identified properties and a derived style rule category that corresponds to the identified properties, the derived style rule category comprises at least one of an inherited property style rule category, a winning property style category, a code style rules category, or a calculated style rule category; displaying at least one of the authored style rules of the authored style rule set for the specific markup language element; and displaying for the specific markup language element, at least one of the derived style rules of the derived style rule set with the at least one of the authored style rules of the authored style rule set, wherein displaying at least one of the derived style rules of the derived style rule set comprises displaying the derived style rule category with each derived style rule, and a description of how values associated with the properties of the derived style rules were derived from the one or more authored style rules.