There are a batch of rules in [[https://phabricator.wikimedia.org/diffusion/SMOD/browse/master/resources/main.css | Modern main.css]] starting with `#mw_content a.external {` and continuing to
```#mw_content a.external[ href$='.pdf' ],
#mw_content a.external[ href$='.PDF' ],
#mw_content a.external[ href*='.pdf#' ],
#mw_content a.external[ href*='.PDF#' ],
#mw_content a.external[ href*='.pdf?' ],
#mw_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 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]].