Quoting from bug 72188:

Intention:
Use certain UI elements, because they are part of the functionality of Wikipedia.

Steps to Reproduce:

1. Set a dark theme for the window manager on Linux
2. Go to (…) the search bar underneath "Search results" when your result is not immediately redirected (These two forms both have the issue - not sure if there are other UI elements that also do).
3. Type any text into the box

Actual Results:

The text is barely readable; dark grey text on a dark grey background.

It seems that .mw-ui-input sets 'color: inherit' without corresponding 'background-color' rule, Special:Search is one of the two places in core where we use it (user login form is the second one).

Version: unspecified
Severity: normal
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=72188