To specify the type of index to generate for HTML or XHTML output:
[Index]
; IndexNavType = HTML (default, plain HTML, uses idxhtm.css),
; CSS (pure CSS, uses idxcss.css), or JavaScript (uses idxjs.*)
IndexNavType = HTML
; WriteIndexCssLink = Yes (default, write link for index CSS) or No
WriteIndexCssLink = Yes
DITA2Go gathers all the index terms from your document into one of three types of multi-level index, depending on the value of IndexNavType:
DITA2Go accesses the required CSS (and JavaScript, if IndexNavType=JavaScript) from %OMSYSHOME%\common\local\htmlidx or, if the files are not there, from %OMSYSHOME%\common\system\htmlidx.
You can copy the CSS and JavaScript files from \system\htmlidx to \local\htmlidx and edit them there, to customize index appearance for your HTML output. Do not change the names of these files, and do not edit the files in %OMSYSHOME%\common\system\htmlidx.
When IndexNavType=HTML, you can also include heading letters across the top of the page, with links to their counterparts within the index. See §14.8.5 Including heading letters in the index.
When WriteIndexCssLink=Yes, DITA2Go writes into the index file <head> the link to the extra CSS file that is called for according to the value of IndexNavType. For example, if IndexNavType=HTML, the link would look like this:
<link rel="stylesheet" href="idxhtm.css"
type="text/css">
WriteIndexCssLink=No is intended to let you turn off the added CSS links for the index, in case you have custom CSS that already includes them, or in case you add your own in-line styles.