fix emoji picker search box background

packages/rocketchat-theme/assets/stylesheets/utils/_colors.import.less

@@ -782,6 +782,12 @@ label.required:after {
 	}
 }
 
+.emoji-filter {
+	input {
+		background-color: @content-background-color;
+	}
+}
+
 input:-webkit-autofill {
 	color: @primary-font-color !important;
 }