Fix issue with help popup rule maching addins search box

rsthemes/nord-polar-night-aurora.rstheme

   color: #d8dee9;
 }
 
-.popupContent div div:nth-child(2) {
+.popupContent:not(.popupMiddleCenterInner) div div:nth-child(2) {
   background: #2e3440 !important;
   border: solid 1px #46597c;
 }

rsthemes/oceanic-plus.rstheme

   color: #D8DEE9;
 }
 
-.popupContent div div:nth-child(2) {
+.popupContent:not(.popupMiddleCenterInner) div div:nth-child(2) {
   background: #1B2B34 !important;
   border: solid 1px #65737E;
 }

rstudio/_rstudio-dark.scss

 .popupContent {
   background: $ui-completions-background;
 	color: $ui-completions-color;
-	& div div:nth-child(2) {
+	&:not(.popupMiddleCenterInner) div div:nth-child(2) {
   	background: $ui-completions-background !important;
   	border: solid 1px $ui-completions-border;
   }