When using the minerva skin on enwiki (and not on other projects such as eswiki or testwiki) the computed stylesheet:
The loaded rule is:
.ns-special h1,
.ns-special h2 {
font-family: -apple-system, 'BlinkMacSystemFont', 'Segoe UI', 'Roboto', 'Lato', 'Helvetica', 'Arial', sans-serif !important
}
The !important enhancer seems over used here, however we are having a hard time determining where this is being introduced to determine why it was introduced.
reported on-wiki in https://en.wikipedia.org/wiki/Wikipedia:Village_pump_(technical)#Elements_in_custom_CSS_disabled