update css for qtconsole in doc

add the .inverted class that is used to show the selected completion

docs/source/interactive/qtconsole.txt

@@ -259,6 +259,8 b' stylesheet:'
     .in-prompt-number { font-weight: bold; }
     .out-prompt { color: darkred; }
     .out-prompt-number { font-weight: bold; }
+    /* .inverted is used to highlight selected completion */
+    .inverted { background-color: black ; color: white; }
 
 Fonts
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