There are a batch of rules in [[https://phabricator.wikimedia.org/diffusion/SMOD/browse/master/resources/main.css | Modern main.css]] starting with `#content a.external {` and continuing to
```#content a.external[ href$='.pdf' ],
#content a.external[ href$='.PDF' ],
#content a.external[ href*='.pdf#' ],
#content a.external[ href*='.PDF#' ],
#content a.external[ href*='.pdf?' ],
#content a.external[ href*='.PDF?' ],
.link-document {
/* @embed */
background: url( images/document.png ) center right no-repeat;
padding-right: 12px;
}```
which should probably reference `.mw-parser-output` instead of `#mw_content`, so that [TemplateStyles](https://www.mediawiki.org/wiki/Extension:TemplateStyles) can reasonably override the default styling. All/the majority of the other skins had this change made. It should be backward compatible with wiki-defined values simply to swap `#mw_content` 1:1 with `.mw-parser-output`, as the wiki-defined values will still be more specific.
Discussion arose in the context of [[https://en.wikipedia.org/wiki/Help_talk:Citation_Style_1#icons_and_the_modern_skin | Help talk:CS1]].