You can specify CSS class names for index entries, for the links from the index into the HTML content, and (though deprecated) for an entry for the index in the table of contents:
[Index] ; IndexLevelClass = class to use for index item <ul>s IndexLevelClass = IndexEntry ; IndexRefClass = class to use for index reference <ul>s IndexRefClass = IndexRef ; IndexTOCClass = class to use for index entry in TOC (deprecated) IndexTOCClass = IndexTOC
These class names are also the names of the respective default formats for each of these features; see §14.8.1 Specifying output formats for the index. In particular, IndexTOCClass is deprecated in favor of IDXTOCFormat.
Note: You can alter the formats by overriding their default definitions; see §7.4.6 Modifying DITA2Go default output formats.
If you want a different appearance (other than indentation) for index entries at each level:
[Index] ; UseIndexLevelNum = No (default) or Yes (include level number ; in IndexLevelClass and IndexRefClass, requires editing CSS). UseIndexLevelNum = Yes
If you set UseIndexLevelNum=Yes, you must also edit the appropriate idx*.css file in \local\htmlidx to include a definition for each level.
The following settings are deprecated in favor of the corresponding format settings:
[Index] ; IndexLetterClass = class for index letters on left (deprecated) IndexLetterClass = IndexLetters ; IndexTopLettersClass = class for index letters at top (deprecated) IndexTopLettersClass = IndexTopLetters
Use IndexLettersFormat and IndexTopLettersFormat instead; see §14.8.5 Including heading letters in the index.