Fontconfig selects Clear Sans as the default serif font.
$ fc-match serif ClearSans-Regular.ttf: "Clear Sans" "Regular"
This seems to be caused by a misconfiguration in fontconfig
/usr/share/fontconfig/conf.avail/60-latin.conf:
<?xml version="1.0"?> <!DOCTYPE fontconfig SYSTEM "fonts.dtd"> <fontconfig> <its:rules xmlns:its="http://www.w3.org/2005/11/its" version="1.0"> <its:translateRule translate="no" selector="/fontconfig/*[not(self::description)]"/> </its:rules> <description>Set preferable fonts for Latin</description> <alias> <family>serif</family> <prefer> <family>Clear Sans</family> [...snip...]
Additionally, the default sans-serif family font is also Clear Sans instead of Noto Sans.
$ fc-match sans-serif ClearSans-Regular.ttf: "Clear Sans" "Regular"