For some reason the CSS seems to be loaded from client side, and the user can see the bar in the left of the page for a few moments before it gets centralized, and hides the list of chapters.

This thread on wikitech may be of some help:
http://www.gossamer-threads.com/lists/wiki/wikitech/363494

From
https://www.mediawiki.org/wiki/Manual:OutputPage.php#JavaScript_and_CSS

"addModuleStyles($modules): Add only CSS of one or more modules recognized by the Resource Loader. Module styles added through this function will be added using standard link CSS tags, rather than as a combined Javascript and CSS package. Thus, they will load even if the user's browser disables JavaScript (unless the browser also disables CSS). $modules can be a module name (string) or an array of module names."

I'm not sure if all the CSS need to be loaded this way, though.

Version: unspecified
Severity: normal