1. A computer-implemented method of transforming a cascading style sheet (“CSS”) codebase for a website, including: using a processor, accessing in memory a CSS codebase that includes target tokens in customizable segments to be customized, responsive to an input invoking a module that uses the CSS codebase; selecting at least one set of customization functions among multiple alternative sets of customization functions that transform the target tokens within the customizable segments of the CSS codebase; scanning the CSS codebase and locating the customizable segments of the CSS codebase that include the target tokens and at least a block of related key-value pairs, customization of the customizable segments of the CSS codebase being located based at least in part on an attribute of a user; parsing, at runtime, only the located customizable segments of the CSS codebase to produce segment parse trees based on the parsed customizable segments; and transforming the target tokens from the segment parse trees according to the selected set of customization functions and outputting a customized codebase to be used with the module invoked by the input.