Each OmniHelp topic file includes in the <head> element a <script> tag that invokes script file ohmain.js. The ohmain.js script calls mainCSS() in parent-frameset script file ohframe.js, which in turn writes a CSS <link> into the topic file.
The CSS <link> in the topic file specifies the value of mainCssName, which is taken from project settings in myproj_ohx.js (see Table 19-2), which are based on [OmniHelpOptions] settings in the configuration file (see §19.4.1 Specifying CSS for topics in OmniHelp). Because the ohframe.js script detects the browser before writing the <link>, the value of mainCssName might depend on what you specified in [OmniHelpOptions] for IECssName, N6CssName, or N4CssName.
As a result, you can see the effects of CSS in topic text only if both of the following are true: