Summary: In dark mode, the current `text-shadow` of a potentially displayed unexpected response output offers a nice fuzzy feeling and is a great alternative to the consumption of beverages. Variables like `{whitetext}` won't work here as it is a PHP file and not CSS. We could introduce a new CSS selector, or remove the text-shadow, or simply hardcode the currently implicit text color (taken from `body`) to black. As there is also a custom background color gradient which does not change either between dark mode and default mode, let's just hardcode the text color. Refs T15056 Test Plan: * Go to http://phorge.localhost/settings/panel/display/ and set `Accessibility` to `Dark Mode (Experimental)` * In `src/aphront/response/AphrontWebpageResponse::buildResponseString()`, override `$unexpected_output` with a custom string * Go to http://phorge.localhost/ and look at the top of the page Reviewers: O1 Blessed Committers, mainframe98 Reviewed By: O1 Blessed Committers, mainframe98 Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno Maniphest Tasks: T15056 Differential Revision: https://we.phorge.it/D26152