Changing the OOUI font size in skinStyles would cause a significant layout shift
because the styles are lazyloaded. OOUI is designed around a based font size of 14px
in mind, so we should obey that. Hopefully WMF will revisit OOUI during T254055, then
this hack can be removed.
--background-color-dp-XX is now fully deprecated in favor of a simpler 4 color surface system. It can be accessed through the --color-surface-X CSS var.