Problem
CodeMirror 6 got rid of the viewportMargin: Infinity option that allowed users to use ⌃+F to search for text within the textarea from outside the textarea. Instead, CM6 gives you a built-in search panel (shown below). This is actually a good thing because it means performance is dramatically better. However, the built-in search panel uses very tiny font, and visually deviates from the designs other UI components in MediaWiki use:
Solution
Provide our own search dialog using CSS-only Codex components. This keeps the implementation small (just changing CSS classes) and won't require us to load all of Codex. Most importantly, it will give the search panel a familiar design that's more consistent with other MW components.
Note also that this search panel is not shown only in WikiEditor (2010). CodeMirror 6 also supports the native 2003 wikitext editor. The 2017 editor has its own search panel and no changes are required there.
Other information
A very similar Community Wishlist proposal was made at https://meta.wikimedia.org/wiki/Community_Wishlist/Wishes/Find_%26_replace. The talk page discussion shows the requester was unhappy with the default WikiEditor (2010) search panel since it obstructs content, which the new CodeMirror search panel won't.
