MediaWiki:Mobile.css is not loaded on the login, create account, or preferences pages. This produces an inconsistent interface on mobile for those with custom styling. On desktop, this problem is fixed by setting $wgAllowSiteCSSOnRestrictedPages to true. However, the value of $wgAllowSiteCSSOnRestrictedPages has no effect on mobile.
The value of $wgAllowSiteCSSOnRestrictedPages should be checked, and if true, then MediaWiki:Mobile.css should be loaded on the login, create account, and preferences special pages.