Ad block is hiding your selector
Why is .ad-inner set to display: none !important? It's because I'm using uBlock Origin, a fantastic ad blocker. It makes the internet tolerable. But it completely breaks the site I'm working on because a previous dev on the project chose ad-inner as a class name.
It turns out, there are a lot of class names that you shouldn't use. Class names, ids, even certain dimensions applied as inline styles. uBlock Origin sources its rules from about 8 different lists, and the list that contained a rule for .ad-inner is EasyList. EasyList is hosted on github and the particular file with selector rules is easylist_general_hide.txt
Here are all the class names in the list that begin with .ad-i
##.ad-icon
##.ad-identifier
##.ad-iframe
##.ad-imagehold
##.ad-img
##.ad-img300X250
##.ad-in-300x250
##.ad-in-content-300
##.ad-in-post
##.ad-in-results
##.ad-incontent-ad-plus-billboard-top
##.ad-incontent-ad-plus-bottom
##.ad-incontent-ad-plus-middle
##.ad-incontent-ad-plus-middle2
##.ad-incontent-ad-plus-middle3
##.ad-incontent-ad-plus-top
##.ad-incontent-wrap
##.ad-index
##.ad-index-main
##.ad-indicator-horiz
##.ad-inline
##.ad-inline-article
##.ad-inner
##.ad-inner-container
##.ad-innr
##.ad-inpage-video-top
##.ad-insert
##.ad-inserter
##.ad-inserter-widget
##.ad-integrated-display
##.ad-internal
##.ad-interruptor
##.ad-interstitial
##.ad-intromercial
##.ad-island
##.ad-item
##.ad-item-related
A good rule of thumb is to not start a class name with .ad. This survey says that 30% of users are using ad blockers.