Hello;
There is a problem in preferences page in the Arabic Wikipedia. This page doesn't accept any styles that can be overwrite in common.css, or vector.css. For example, if I want to change the font-family of Wikipedia locally in my vector.css, it will change in all the website pages, but not shown in preferences page. Now, In Arabic Wikipedia, the default font is sans-serif, but it's overwritten to be Arial in common.css. But this font not work in preferences page. Here is the code which change the font in common.css:

html,body,
#content h1,#content h2,#content #firstHeading,
.mw-body .mw-editsection, .mw-body .mw-editsection-like,.ui-widget,
.mw-body #toc h2, .mw-body .toc h2,
.flow-topic-title,h2.flow-board-header-title,
.mw-collapsible-toggle, .mw-collapsible-toggle > a,.CategoryTreeToggle,.CategoryTreeEmptyBullet,.NavToggle{
font-family: Arial;
}

And if you check all pages in Arabic wikipedia; you'll find the font changed in all pages; except Preferences page. When I inspect element in google chrome, and looking for the source of font-family property, it says it come from this link: https://goo.gl/HjefKm. What I'm ask for is how can I overwrite the font-family property of the prefernces page?.