docs: repair dark theme search styling (#1080)

Author: bhavyagosai

www/src/css/custom.css

@@ -40,6 +40,10 @@
   background-color: rgba(0, 0, 0, 0.3);
 }
 
+[data-theme='dark'] .DocSearch {
+  --docsearch-hit-active-color: black;
+}
+
 /* skip for home page and v4 docs */
 html.plugin-id-default.plugin-pages div[class*="announcementBar"],
 html[class*="docs-version-4"] div[class*="announcementBar"] {